Commit Graph

526 Commits

Author SHA1 Message Date
Linus Torvalds 7140ad3898 Updates for v4.19:
- Restructure of lockdep and latency tracers
 
    This is the biggest change. Joel Fernandes restructured the hooks
    from irqs and preemption disabling and enabling. He got rid of
    a lot of the preprocessor #ifdef mess that they caused.
 
    He turned both lockdep and the latency tracers to use trace events
    inserted in the preempt/irqs disabling paths. But unfortunately,
    these started to cause issues in corner cases. Thus, parts of the
    code was reverted back to where lockde and the latency tracers
    just get called directly (without using the trace events).
    But because the original change cleaned up the code very nicely
    we kept that, as well as the trace events for preempt and irqs
    disabling, but they are limited to not being called in NMIs.
 
  - Have trace events use SRCU for "rcu idle" calls. This was required
    for the preempt/irqs off trace events. But it also had to not
    allow them to be called in NMI context. Waiting till Paul makes
    an NMI safe SRCU API.
 
  - New notrace SRCU API to allow trace events to use SRCU.
 
  - Addition of mcount-nop option support
 
  - SPDX headers replacing GPL templates.
 
  - Various other fixes and clean ups.
 
  - Some fixes are marked for stable, but were not fully tested
    before the merge window opened.
 -----BEGIN PGP SIGNATURE-----
 
 iIoEABYIADIWIQRRSw7ePDh/lE+zeZMp5XQQmuv6qgUCW3ruhRQccm9zdGVkdEBn
 b29kbWlzLm9yZwAKCRAp5XQQmuv6qiM7AP47NhYdSnCFCRUJfrt6PovXmQtuCHt3
 c3QMoGGdvzh9YAEAqcSXwh7uLhpHUp1LjMAPkXdZVwNddf4zJQ1zyxQ+EAU=
 =vgEr
 -----END PGP SIGNATURE-----

Merge tag 'trace-v4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:

 - Restructure of lockdep and latency tracers

   This is the biggest change. Joel Fernandes restructured the hooks
   from irqs and preemption disabling and enabling. He got rid of a lot
   of the preprocessor #ifdef mess that they caused.

   He turned both lockdep and the latency tracers to use trace events
   inserted in the preempt/irqs disabling paths. But unfortunately,
   these started to cause issues in corner cases. Thus, parts of the
   code was reverted back to where lockdep and the latency tracers just
   get called directly (without using the trace events). But because the
   original change cleaned up the code very nicely we kept that, as well
   as the trace events for preempt and irqs disabling, but they are
   limited to not being called in NMIs.

 - Have trace events use SRCU for "rcu idle" calls. This was required
   for the preempt/irqs off trace events. But it also had to not allow
   them to be called in NMI context. Waiting till Paul makes an NMI safe
   SRCU API.

 - New notrace SRCU API to allow trace events to use SRCU.

 - Addition of mcount-nop option support

 - SPDX headers replacing GPL templates.

 - Various other fixes and clean ups.

 - Some fixes are marked for stable, but were not fully tested before
   the merge window opened.

* tag 'trace-v4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (44 commits)
  tracing: Fix SPDX format headers to use C++ style comments
  tracing: Add SPDX License format tags to tracing files
  tracing: Add SPDX License format to bpf_trace.c
  blktrace: Add SPDX License format header
  s390/ftrace: Add -mfentry and -mnop-mcount support
  tracing: Add -mcount-nop option support
  tracing: Avoid calling cc-option -mrecord-mcount for every Makefile
  tracing: Handle CC_FLAGS_FTRACE more accurately
  Uprobe: Additional argument arch_uprobe to uprobe_write_opcode()
  Uprobes: Simplify uprobe_register() body
  tracepoints: Free early tracepoints after RCU is initialized
  uprobes: Use synchronize_rcu() not synchronize_sched()
  tracing: Fix synchronizing to event changes with tracepoint_synchronize_unregister()
  ftrace: Remove unused pointer ftrace_swapper_pid
  tracing: More reverting of "tracing: Centralize preemptirq tracepoints and unify their usage"
  tracing/irqsoff: Handle preempt_count for different configs
  tracing: Partial revert of "tracing: Centralize preemptirq tracepoints and unify their usage"
  tracing: irqsoff: Account for additional preempt_disable
  trace: Use rcu_dereference_raw for hooks from trace-event subsystem
  tracing/kprobes: Fix within_notrace_func() to check only notrace functions
  ...
2018-08-20 18:32:00 -07:00
Linus Torvalds 54dbe75bbf drm pull for 4.19-rc1
-----BEGIN PGP SIGNATURE-----
 
 iQIcBAABAgAGBQJbc41pAAoJEAx081l5xIa+ZrAP/AzKj4i4pBLVJcvNZ2BwD+UD
 ZNSNj2iqCJ5+Jo/WtIwQ8tLct9UqfVssUwBke6tZksiLdTigGPTUyVIAdK+9kyWD
 D00m3x/pToJrSF2D0FwxQlPUtPkohp9N+E6+TU7gd1oCasZfBzmcEpoVAmZf+NWE
 kN1xXpmGxZWpu0wc7JA2lv9MuUTijCwIqJqa5E0bB3z06G5mw+PJ89kYzMx19OyA
 ZYQK8y3A40ZGl8UbajZ4xg9pqFCRYFFHGqfYlpUWWTh0XMAXu8+Yqzh3dJxmak7r
 4u2pdQBsxPMZO8qKBHpVvI7Zhoe0Ntnolc0XVD+2IbqqnTprVbQs0bWf3YyfUlQi
 1/9bWFK67W0LEuzac6M7a7EQqFNiHF13Btao7aqENTIe/GaCZJoopaiRMAmh6EHD
 4PezeYqrW8cSaPj6OKouL1BhW9Bjixsg0bvjS/uB6m4KekFCt1++BDFGzkqvm6Mo
 SVW7nkJoCFpCASaR7DhUEOPexaHeJ65HCDDUvYdqz9jd2w1TgvvanEZWual1NwEm
 ImA8A4wGZ/3KijpyyKm0gE96RX7+zMMZ3brW6p1vhUUKVYJCrvSr5jrXH5+2k6Aw
 Y455doGL87IRkwyje/YbQF0I8pbUZD9QS5wII13tLGwOH9/uC/Xl6dHNM40gtqyh
 W4gEdY+NAMJmYLvRNawa
 =g9rD
 -----END PGP SIGNATURE-----

Merge tag 'drm-next-2018-08-15' of git://anongit.freedesktop.org/drm/drm

Pull drm updates from Dave Airlie:
 "This is the main drm pull request for 4.19.

  Rob has some new hardware support for new qualcomm hw that I'll send
  along separately. This has the display part of it, the remaining pull
  is for the acceleration engine.

  This also contains a wound-wait/wait-die mutex rework, Peter has acked
  it for merging via my tree.

  Otherwise mostly the usual level of activity. Summary:

  core:
   - Wound-wait/wait-die mutex rework
   - Add writeback connector type
   - Add "content type" property for HDMI
   - Move GEM bo to drm_framebuffer
   - Initial gpu scheduler documentation
   - GPU scheduler fixes for dying processes
   - Console deferred fbcon takeover support
   - Displayport support for CEC tunneling over AUX

  panel:
   - otm8009a panel driver fixes
   - Innolux TV123WAM and G070Y2-L01 panel driver
   - Ilitek ILI9881c panel driver
   - Rocktech RK070ER9427 LCD
   - EDT ETM0700G0EDH6 and EDT ETM0700G0BDH6
   - DLC DLC0700YZG-1
   - BOE HV070WSA-100
   - newhaven, nhd-4.3-480272ef-atxl LCD
   - DataImage SCF0700C48GGU18
   - Sharp LQ035Q7DB03
   - p079zca: Refactor to support multiple panels

  tinydrm:
   - ILI9341 display panel

  New driver:
   - vkms - virtual kms driver to testing.

  i915:
   - Icelake:
        Display enablement
        DSI support
        IRQ support
        Powerwell support
   - GPU reset fixes and improvements
   - Full ppgtt support refactoring
   - PSR fixes and improvements
   - Execlist improvments
   - GuC related fixes

  amdgpu:
   - Initial amdgpu documentation
   - JPEG engine support on VCN
   - CIK uses powerplay by default
   - Move to using core PCIE functionality for gens/lanes
   - DC/Powerplay interface rework
   - Stutter mode support for RV
   - Vega12 Powerplay updates
   - GFXOFF fixes
   - GPUVM fault debugging
   - Vega12 GFXOFF
   - DC improvements
   - DC i2c/aux changes
   - UVD 7.2 fixes
   - Powerplay fixes for Polaris12, CZ/ST
   - command submission bo_list fixes

  amdkfd:
   - Raven support
   - Power management fixes

  udl:
   - Cleanups and fixes

  nouveau:
   - misc fixes and cleanups.

  msm:
   - DPU1 support display controller in sdm845
   - GPU coredump support.

  vmwgfx:
   - Atomic modesetting validation fixes
   - Support for multisample surfaces

  armada:
   - Atomic modesetting support completed.

  exynos:
   - IPPv2 fixes
   - Move g2d to component framework
   - Suspend/resume support cleanups
   - Driver cleanups

  imx:
   - CSI configuration improvements
   - Driver cleanups
   - Use atomic suspend/resume helpers
   - ipu-v3 V4L2 XRGB32/XBGR32 support

  pl111:
   - Add Nomadik LCDC variant

  v3d:
   - GPU scheduler jobs management

  sun4i:
   - R40 display engine support
   - TCON TOP driver

  mediatek:
   - MT2712 SoC support

  rockchip:
   - vop fixes

  omapdrm:
   - Workaround for DRA7 errata i932
   - Fix mm_list locking

  mali-dp:
   - Writeback implementation
        PM improvements
   - Internal error reporting debugfs

  tilcdc:
   - Single fix for deferred probing

  hdlcd:
   - Teardown fixes

  tda998x:
   - Converted to a bridge driver.

  etnaviv:
   - Misc fixes"

* tag 'drm-next-2018-08-15' of git://anongit.freedesktop.org/drm/drm: (1506 commits)
  drm/amdgpu/sriov: give 8s for recover vram under RUNTIME
  drm/scheduler: fix param documentation
  drm/i2c: tda998x: correct PLL divider calculation
  drm/i2c: tda998x: get rid of private fill_modes function
  drm/i2c: tda998x: move mode_valid() to bridge
  drm/i2c: tda998x: register bridge outside of component helper
  drm/i2c: tda998x: cleanup from previous changes
  drm/i2c: tda998x: allocate tda998x_priv inside tda998x_create()
  drm/i2c: tda998x: convert to bridge driver
  drm/scheduler: fix timeout worker setup for out of order job completions
  drm/amd/display: display connected to dp-1 does not light up
  drm/amd/display: update clk for various HDMI color depths
  drm/amd/display: program display clock on cache match
  drm/amd/display: Add NULL check for enabling dp ss
  drm/amd/display: add vbios table check for enabling dp ss
  drm/amd/display: Don't share clk source between DP and HDMI
  drm/amd/display: Fix DP HBR2 Eye Diagram Pattern on Carrizo
  drm/amd/display: Use calculated disp_clk_khz value for dce110
  drm/amd/display: Implement custom degamma lut on dcn
  drm/amd/display: Destroy aux_engines only once
  ...
2018-08-15 17:39:07 -07:00
Linus Torvalds b99cdfdf0b Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU updates from Thomas Gleixner:
 "A large update to RCU:

  Preparatory work for consolidating the RCU flavors:

   - Introduce grace-period sequence numbers to the RCU-bh, RCU-preempt,
     and RCU-sched flavors, replacing the old ->gpnum and ->completed
     pair of fields.

     This change allows lockless code to obtain the complete
     grace-period state with a single READ_ONCE(), which is needed to
     maintain tolerable lock contention during the upcoming
     consolidation of the three RCU flavors.

     Note that grace-period sequence numbers are already used by
     rcu_barrier(), expedited RCU grace periods, and SRCU, and are thus
     already heavily used and well-tested. Joel Fernandes contributed a
     number of excellent fixes and improvements.

   - Clean up some grace-period-reporting loose ends, including
     improving the handling of quiescent states from offline CPUs and
     fixing some false-positive WARN_ON_ONCE() invocations.

     (Strictly speaking, the WARN_ON_ONCE() invocations were quite
     correct, but their invariants were (harmlessly) violated by the
     earlier sloppy handling of quiescent states from offline CPUs.)

     In addition, improve grace-period forward-progress guarantees so as
     to allow removal of fail-safe checks that required otherwise
     needless lock acquisitions. Finally, add more diagnostics to help
     debug the upcoming consolidation of the RCU-bh, RCU-preempt, and
     RCU-sched flavors.

  The rest:

   - SRCU updates

   - Updates to rcutorture and associated scripting.

   - The usual pile of miscellaneous fixes"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (118 commits)
  rcutorture: Fix rcu_barrier successes counter
  rcutorture: Add support to detect if boost kthread prio is too low
  rcutorture: Use monotonic timestamp for stall detection
  rcutorture: Make boost test more robust
  rcutorture: Disable RT throttling for boost tests
  rcutorture: Emphasize testing of single reader protection type
  rcutorture: Handle extended read-side critical sections
  rcutorture: Make rcu_torture_timer() use rcu_torture_one_read()
  rcutorture: Use per-CPU random state for rcu_torture_timer()
  rcutorture: Use atomic increment for n_rcu_torture_timers
  rcutorture: Extract common code from rcu_torture_reader()
  rcuperf: Remove unused torturing_tasks() function
  rcu: Remove rcutorture test version and sequence number
  rcutorture: Change units of onoff_interval to jiffies
  rcu: Assign higher prio to RCU threads if rcutorture is built-in
  rculist: Improve documentation for list_for_each_entry_from_rcu()
  srcu: Add grace-period number to rcutorture statistics printout
  rcu: Print stall-warning NMI dyntick state in hexadecimal
  MAINTAINERS: Update RCU, SRCU, and TORTURE-TEST entries
  rcu: Make rcu_seq_diff() more exact
  ...
2018-08-13 10:49:41 -07:00
Steven Rostedt (VMware) bff1b208a5 tracing: Partial revert of "tracing: Centralize preemptirq tracepoints and unify their usage"
Joel Fernandes created a nice patch that cleaned up the duplicate hooks used
by lockdep and irqsoff latency tracer. It made both use tracepoints. But it
caused lockdep to trigger several false positives. We have not figured out
why yet, but removing lockdep from using the trace event hooks and just call
its helper functions directly (like it use to), makes the problem go away.

This is a partial revert of the clean up patch c3bc8fd637 ("tracing:
Centralize preemptirq tracepoints and unify their usage") that adds direct
calls for lockdep, but also keeps most of the clean up done to get rid of
the horrible preprocessor if statements.

Link: http://lkml.kernel.org/r/20180806155058.5ee875f4@gandalf.local.home

Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Fixes: c3bc8fd637 ("tracing: Centralize preemptirq tracepoints and unify their usage")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2018-08-10 15:11:25 -04:00
Joel Fernandes (Google) c3bc8fd637 tracing: Centralize preemptirq tracepoints and unify their usage
This patch detaches the preemptirq tracepoints from the tracers and
keeps it separate.

Advantages:
* Lockdep and irqsoff event can now run in parallel since they no longer
have their own calls.

* This unifies the usecase of adding hooks to an irqsoff and irqson
event, and a preemptoff and preempton event.
  3 users of the events exist:
  - Lockdep
  - irqsoff and preemptoff tracers
  - irqs and preempt trace events

The unification cleans up several ifdefs and makes the code in preempt
tracer and irqsoff tracers simpler. It gets rid of all the horrific
ifdeferry around PROVE_LOCKING and makes configuration of the different
users of the tracepoints more easy and understandable. It also gets rid
of the time_* function calls from the lockdep hooks used to call into
the preemptirq tracer which is not needed anymore. The negative delta in
lines of code in this patch is quite large too.

In the patch we introduce a new CONFIG option PREEMPTIRQ_TRACEPOINTS
as a single point for registering probes onto the tracepoints. With
this,
the web of config options for preempt/irq toggle tracepoints and its
users becomes:

 PREEMPT_TRACER   PREEMPTIRQ_EVENTS  IRQSOFF_TRACER PROVE_LOCKING
       |                 |     \         |           |
       \    (selects)    /      \        \ (selects) /
      TRACE_PREEMPT_TOGGLE       ----> TRACE_IRQFLAGS
                      \                  /
                       \ (depends on)   /
                     PREEMPTIRQ_TRACEPOINTS

Other than the performance tests mentioned in the previous patch, I also
ran the locking API test suite. I verified that all tests cases are
passing.

I also injected issues by not registering lockdep probes onto the
tracepoints and I see failures to confirm that the probes are indeed
working.

This series + lockdep probes not registered (just to inject errors):
[    0.000000]      hard-irqs-on + irq-safe-A/21:  ok  |  ok  |  ok  |
[    0.000000]      soft-irqs-on + irq-safe-A/21:  ok  |  ok  |  ok  |
[    0.000000]        sirq-safe-A => hirqs-on/12:FAILED|FAILED|  ok  |
[    0.000000]        sirq-safe-A => hirqs-on/21:FAILED|FAILED|  ok  |
[    0.000000]          hard-safe-A + irqs-on/12:FAILED|FAILED|  ok  |
[    0.000000]          soft-safe-A + irqs-on/12:FAILED|FAILED|  ok  |
[    0.000000]          hard-safe-A + irqs-on/21:FAILED|FAILED|  ok  |
[    0.000000]          soft-safe-A + irqs-on/21:FAILED|FAILED|  ok  |
[    0.000000]     hard-safe-A + unsafe-B #1/123:  ok  |  ok  |  ok  |
[    0.000000]     soft-safe-A + unsafe-B #1/123:  ok  |  ok  |  ok  |

With this series + lockdep probes registered, all locking tests pass:

[    0.000000]      hard-irqs-on + irq-safe-A/21:  ok  |  ok  |  ok  |
[    0.000000]      soft-irqs-on + irq-safe-A/21:  ok  |  ok  |  ok  |
[    0.000000]        sirq-safe-A => hirqs-on/12:  ok  |  ok  |  ok  |
[    0.000000]        sirq-safe-A => hirqs-on/21:  ok  |  ok  |  ok  |
[    0.000000]          hard-safe-A + irqs-on/12:  ok  |  ok  |  ok  |
[    0.000000]          soft-safe-A + irqs-on/12:  ok  |  ok  |  ok  |
[    0.000000]          hard-safe-A + irqs-on/21:  ok  |  ok  |  ok  |
[    0.000000]          soft-safe-A + irqs-on/21:  ok  |  ok  |  ok  |
[    0.000000]     hard-safe-A + unsafe-B #1/123:  ok  |  ok  |  ok  |
[    0.000000]     soft-safe-A + unsafe-B #1/123:  ok  |  ok  |  ok  |

Link: http://lkml.kernel.org/r/20180730222423.196630-4-joel@joelfernandes.org

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2018-07-31 11:32:27 -04:00
Joel Fernandes (Google) 01f38497c6 lockdep: Use this_cpu_ptr instead of get_cpu_var stats
get_cpu_var disables preemption which has the potential to call into the
preemption disable trace points causing some complications. There's also
no need to disable preemption in uses of get_lock_stats anyway since
preempt is already disabled. So lets simplify the code.

Link: http://lkml.kernel.org/r/20180730222423.196630-2-joel@joelfernandes.org

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2018-07-30 19:06:54 -04:00
Peter Rosin 62cedf3e60 locking/rtmutex: Allow specifying a subclass for nested locking
Needed for annotating rt_mutex locks.

Tested-by: John Sperbeck <jsperbeck@google.com>
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Deepa Dinamani <deepadinamani@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Chang <dpf@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Wolfram Sang <wsa@the-dreams.de>
Link: http://lkml.kernel.org/r/20180720083914.1950-2-peda@axentia.se
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-25 11:22:19 +02:00
Ingo Molnar ea73a5c692 Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu
Pull RCU updates from Paul E. McKenney:

- An optimization and a fix for RCU expedited grace periods, with
  the fix being from Boqun Feng.

- Miscellaneous fixes, including a lockdep-annotation fix from
  Boqun Feng.

- SRCU updates.

- Updates to rcutorture and associated scripting.

- Introduce grace-period sequence numbers to the RCU-bh, RCU-preempt,
  and RCU-sched flavors, replacing the old ->gpnum and ->completed
  pair of fields.  This change allows lockless code to obtain the
  complete grace-period state with a single READ_ONCE(), which is
  needed to maintain tolerable lock contention during the upcoming
  consolidation of the three RCU flavors.  Note that grace-period
  sequence numbers are already used by rcu_barrier(), expedited
  RCU grace periods, and SRCU, and are thus already heavily used
  and well-tested.  Joel Fernandes contributed a number of excellent
  fixes and improvements.

- Clean up some grace-period-reporting loose ends, including
  improving the handling of quiescent states from offline CPUs
  and fixing some false-positive WARN_ON_ONCE() invocations.
  (Strictly speaking, the WARN_ON_ONCE() invocations were quite
  correct, but their invariants were (harmlessly) violated by the
  earlier sloppy handling of quiescent states from offline CPUs.)
  In addition, improve grace-period forward-progress guarantees so
  as to allow removal of fail-safe checks that required otherwise
  needless lock acquisitions.  Finally, add more diagnostics to
  help debug the upcoming consolidation of the RCU-bh, RCU-preempt,
  and RCU-sched flavors.

- Additional miscellaneous fixes, including those contributed by
  Byungchul Park, Mauro Carvalho Chehab, Joe Perches, Joel Fernandes,
  Steven Rostedt, Andrea Parri, and Neil Brown.

- Additional torture-test changes, including several contributed by
  Arnd Bergmann and Joel Fernandes.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-17 09:16:02 +02:00
Dave Airlie c5be9b5403 Merge branch 'vmwgfx-next' of git://people.freedesktop.org/~thomash/linux into drm-next
A patchset worked out together with Peter Zijlstra. Ingo is OK with taking
it through the DRM tree:

This is a small fallout from a work to allow batching WW mutex locks and
unlocks.

Our Wound-Wait mutexes actually don't use the Wound-Wait algorithm but
the Wait-Die algorithm. One could perhaps rename those mutexes tree-wide to
"Wait-Die mutexes" or "Deadlock Avoidance mutexes". Another approach suggested
here is to implement also the "Wound-Wait" algorithm as a per-WW-class
choice, as it has advantages in some cases. See for example

http://www.mathcs.emory.edu/~cheung/Courses/554/Syllabus/8-recv+serial/deadlock-compare.html

Now Wound-Wait is a preemptive algorithm, and the preemption is implemented
using a lazy scheme: If a wounded transaction is about to go to sleep on
a contended WW mutex, we return -EDEADLK. That is sufficient for deadlock
prevention. Since with WW mutexes we also require the aborted transaction to
sleep waiting to lock the WW mutex it was aborted on, this choice also provides
a suitable WW mutex to sleep on. If we were to return -EDEADLK on the first
WW mutex lock after the transaction was wounded whether the WW mutex was
contended or not, the transaction might frequently be restarted without a wait,
which is far from optimal. Note also that with the lazy preemption scheme,
contrary to Wait-Die there will be no rollbacks on lock contention of locks
held by a transaction that has completed its locking sequence.

The modeset locks are then changed from Wait-Die to Wound-Wait since the
typical locking pattern of those locks very well matches the criterion for
a substantial reduction in the number of rollbacks. For reservation objects,
the benefit is more unclear at this point and they remain using Wait-Die.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703105339.4461-1-thellstrom@vmware.com
2018-07-06 08:47:14 +10:00
Thomas Hellstrom 08295b3b5b locking: Implement an algorithm choice for Wound-Wait mutexes
The current Wound-Wait mutex algorithm is actually not Wound-Wait but
Wait-Die. Implement also Wound-Wait as a per-ww-class choice. Wound-Wait
is, contrary to Wait-Die a preemptive algorithm and is known to generate
fewer backoffs. Testing reveals that this is true if the
number of simultaneous contending transactions is small.
As the number of simultaneous contending threads increases, Wait-Wound
becomes inferior to Wait-Die in terms of elapsed time.
Possibly due to the larger number of held locks of sleeping transactions.

Update documentation and callers.

Timings using git://people.freedesktop.org/~thomash/ww_mutex_test
tag patch-18-06-15

Each thread runs 100000 batches of lock / unlock 800 ww mutexes randomly
chosen out of 100000. Four core Intel x86_64:

Algorithm    #threads       Rollbacks  time
Wound-Wait   4              ~100       ~17s.
Wait-Die     4              ~150000    ~19s.
Wound-Wait   16             ~360000    ~109s.
Wait-Die     16             ~450000    ~82s.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
2018-07-03 09:44:36 +02:00
Peter Ziljstra 55f036ca7e locking: WW mutex cleanup
Make the WW mutex code more readable by adding comments, splitting up
functions and pointing out that we're actually using the Wait-Die
algorithm.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
2018-07-03 09:42:40 +02:00
Paul E. McKenney 6050003763 torture: Keep old-school dmesg format
This commit adds "#define pr_fmt(fmt) fmt" to the torture-test files
in order to keep the current dmesg format.  Once Joe's commits have
hit mainline, these definitions will be changed in order to automatically
generate the dmesg line prefix that the scripts expect.  This will have
the beneficial side-effect of allowing printk() formats to be used more
widely and of shortening some pr_*() lines.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Joe Perches <joe@perches.com>
2018-06-25 11:30:10 -07:00
Paul E. McKenney 90127d605f torture: Make online/offline messages appear only for verbose=2
Some bugs reproduce quickly only at high CPU-hotplug rates, so the
rcutorture TREE03 scenario now has only 200 milliseconds spacing between
CPU-hotplug operations.  At this rate, the torture-test pair of console
messages per operation becomes a bit voluminous.  This commit therefore
converts the torture-test set of "verbose" kernel-boot arguments from
bool to int, and prints the extra console messages only when verbose=2.
The default is still verbose=1.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-06-25 11:30:10 -07:00
Linus Torvalds 2da2ca24a3 Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Thomas Gleixner:
 "A set of fixes and updates for the locking code:

   - Prevent lockdep from updating irq state within its own code and
     thereby confusing itself.

   - Buid fix for older GCCs which mistreat anonymous unions

   - Add a missing lockdep annotation in down_read_non_onwer() which
     causes up_read_non_owner() to emit a lockdep splat

   - Remove the custom alpha dec_and_lock() implementation which is
     incorrect in terms of ordering and use the generic one.

  The remaining two commits are not strictly fixes. They provide irqsave
  variants of atomic_dec_and_lock() and refcount_dec_and_lock(). These
  are required to merge the relevant updates and cleanups into different
  maintainer trees for 4.19, so routing them into mainline without
  actual users is the sanest approach.

  They should have been in -rc1, but last weekend I took the liberty to
  just avoid computers in order to regain some mental sanity"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/qspinlock: Fix build for anonymous union in older GCC compilers
  locking/lockdep: Do not record IRQ state within lockdep code
  locking/rwsem: Fix up_read_non_owner() warning with DEBUG_RWSEMS
  locking/refcounts: Implement refcount_dec_and_lock_irqsave()
  atomic: Add irqsave variant of atomic_dec_and_lock()
  alpha: Remove custom dec_and_lock() implementation
2018-06-24 19:36:16 +08:00
Steven Rostedt (VMware) fcc784be83 locking/lockdep: Do not record IRQ state within lockdep code
While debugging where things were going wrong with mapping
enabling/disabling interrupts with the lockdep state and actual real
enabling and disabling interrupts, I had to silent the IRQ
disabling/enabling in debug_check_no_locks_freed() because it was
always showing up as it was called before the splat was.

Use raw_local_irq_save/restore() for not only debug_check_no_locks_freed()
but for all internal lockdep functions, as they hide useful information
about where interrupts were used incorrectly last.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/lkml/20180404140630.3f4f4c7a@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-06-21 18:19:01 +02:00
Waiman Long 03eeafdd9a locking/rwsem: Fix up_read_non_owner() warning with DEBUG_RWSEMS
It was found that the use of up_read_non_owner() in NFS was causing
the following warning when DEBUG_RWSEMS was configured.

  DEBUG_LOCKS_WARN_ON(sem->owner != ((struct task_struct *)(1UL << 0)))

Looking into the rwsem.c file, it was discovered that the corresponding
down_read_non_owner() function was not setting the owner field properly.
This is fixed now, and the warning should be gone.

Fixes: 5149cbac42 ("locking/rwsem: Add DEBUG_RWSEMS to look for lock/unlock mismatches")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Gavin Schenk <g.schenk@eckelmann.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-nfs@vger.kernel.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1527168398-4291-1-git-send-email-longman@redhat.com
2018-06-20 11:29:23 +02:00
Kees Cook 6396bb2215 treewide: kzalloc() -> kcalloc()
The kzalloc() function has a 2-factor argument form, kcalloc(). This
patch replaces cases of:

        kzalloc(a * b, gfp)

with:
        kcalloc(a * b, gfp)

as well as handling cases of:

        kzalloc(a * b * c, gfp)

with:

        kzalloc(array3_size(a, b, c), gfp)

as it's slightly less ugly than:

        kzalloc_array(array_size(a, b), c, gfp)

This does, however, attempt to ignore constant size factors like:

        kzalloc(4 * 1024, gfp)

though any constants defined via macros get caught up in the conversion.

Any factors with a sizeof() of "unsigned char", "char", and "u8" were
dropped, since they're redundant.

The Coccinelle script used for this was:

// Fix redundant parens around sizeof().
@@
type TYPE;
expression THING, E;
@@

(
  kzalloc(
-	(sizeof(TYPE)) * E
+	sizeof(TYPE) * E
  , ...)
|
  kzalloc(
-	(sizeof(THING)) * E
+	sizeof(THING) * E
  , ...)
)

// Drop single-byte sizes and redundant parens.
@@
expression COUNT;
typedef u8;
typedef __u8;
@@

(
  kzalloc(
-	sizeof(u8) * (COUNT)
+	COUNT
  , ...)
|
  kzalloc(
-	sizeof(__u8) * (COUNT)
+	COUNT
  , ...)
|
  kzalloc(
-	sizeof(char) * (COUNT)
+	COUNT
  , ...)
|
  kzalloc(
-	sizeof(unsigned char) * (COUNT)
+	COUNT
  , ...)
|
  kzalloc(
-	sizeof(u8) * COUNT
+	COUNT
  , ...)
|
  kzalloc(
-	sizeof(__u8) * COUNT
+	COUNT
  , ...)
|
  kzalloc(
-	sizeof(char) * COUNT
+	COUNT
  , ...)
|
  kzalloc(
-	sizeof(unsigned char) * COUNT
+	COUNT
  , ...)
)

// 2-factor product with sizeof(type/expression) and identifier or constant.
@@
type TYPE;
expression THING;
identifier COUNT_ID;
constant COUNT_CONST;
@@

(
- kzalloc
+ kcalloc
  (
-	sizeof(TYPE) * (COUNT_ID)
+	COUNT_ID, sizeof(TYPE)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(TYPE) * COUNT_ID
+	COUNT_ID, sizeof(TYPE)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(TYPE) * (COUNT_CONST)
+	COUNT_CONST, sizeof(TYPE)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(TYPE) * COUNT_CONST
+	COUNT_CONST, sizeof(TYPE)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(THING) * (COUNT_ID)
+	COUNT_ID, sizeof(THING)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(THING) * COUNT_ID
+	COUNT_ID, sizeof(THING)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(THING) * (COUNT_CONST)
+	COUNT_CONST, sizeof(THING)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(THING) * COUNT_CONST
+	COUNT_CONST, sizeof(THING)
  , ...)
)

// 2-factor product, only identifiers.
@@
identifier SIZE, COUNT;
@@

- kzalloc
+ kcalloc
  (
-	SIZE * COUNT
+	COUNT, SIZE
  , ...)

// 3-factor product with 1 sizeof(type) or sizeof(expression), with
// redundant parens removed.
@@
expression THING;
identifier STRIDE, COUNT;
type TYPE;
@@

(
  kzalloc(
-	sizeof(TYPE) * (COUNT) * (STRIDE)
+	array3_size(COUNT, STRIDE, sizeof(TYPE))
  , ...)
|
  kzalloc(
-	sizeof(TYPE) * (COUNT) * STRIDE
+	array3_size(COUNT, STRIDE, sizeof(TYPE))
  , ...)
|
  kzalloc(
-	sizeof(TYPE) * COUNT * (STRIDE)
+	array3_size(COUNT, STRIDE, sizeof(TYPE))
  , ...)
|
  kzalloc(
-	sizeof(TYPE) * COUNT * STRIDE
+	array3_size(COUNT, STRIDE, sizeof(TYPE))
  , ...)
|
  kzalloc(
-	sizeof(THING) * (COUNT) * (STRIDE)
+	array3_size(COUNT, STRIDE, sizeof(THING))
  , ...)
|
  kzalloc(
-	sizeof(THING) * (COUNT) * STRIDE
+	array3_size(COUNT, STRIDE, sizeof(THING))
  , ...)
|
  kzalloc(
-	sizeof(THING) * COUNT * (STRIDE)
+	array3_size(COUNT, STRIDE, sizeof(THING))
  , ...)
|
  kzalloc(
-	sizeof(THING) * COUNT * STRIDE
+	array3_size(COUNT, STRIDE, sizeof(THING))
  , ...)
)

// 3-factor product with 2 sizeof(variable), with redundant parens removed.
@@
expression THING1, THING2;
identifier COUNT;
type TYPE1, TYPE2;
@@

(
  kzalloc(
-	sizeof(TYPE1) * sizeof(TYPE2) * COUNT
+	array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
  , ...)
|
  kzalloc(
-	sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+	array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
  , ...)
|
  kzalloc(
-	sizeof(THING1) * sizeof(THING2) * COUNT
+	array3_size(COUNT, sizeof(THING1), sizeof(THING2))
  , ...)
|
  kzalloc(
-	sizeof(THING1) * sizeof(THING2) * (COUNT)
+	array3_size(COUNT, sizeof(THING1), sizeof(THING2))
  , ...)
|
  kzalloc(
-	sizeof(TYPE1) * sizeof(THING2) * COUNT
+	array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
  , ...)
|
  kzalloc(
-	sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+	array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
  , ...)
)

// 3-factor product, only identifiers, with redundant parens removed.
@@
identifier STRIDE, SIZE, COUNT;
@@

(
  kzalloc(
-	(COUNT) * STRIDE * SIZE
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kzalloc(
-	COUNT * (STRIDE) * SIZE
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kzalloc(
-	COUNT * STRIDE * (SIZE)
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kzalloc(
-	(COUNT) * (STRIDE) * SIZE
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kzalloc(
-	COUNT * (STRIDE) * (SIZE)
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kzalloc(
-	(COUNT) * STRIDE * (SIZE)
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kzalloc(
-	(COUNT) * (STRIDE) * (SIZE)
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kzalloc(
-	COUNT * STRIDE * SIZE
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
)

// Any remaining multi-factor products, first at least 3-factor products,
// when they're not all constants...
@@
expression E1, E2, E3;
constant C1, C2, C3;
@@

(
  kzalloc(C1 * C2 * C3, ...)
|
  kzalloc(
-	(E1) * E2 * E3
+	array3_size(E1, E2, E3)
  , ...)
|
  kzalloc(
-	(E1) * (E2) * E3
+	array3_size(E1, E2, E3)
  , ...)
|
  kzalloc(
-	(E1) * (E2) * (E3)
+	array3_size(E1, E2, E3)
  , ...)
|
  kzalloc(
-	E1 * E2 * E3
+	array3_size(E1, E2, E3)
  , ...)
)

// And then all remaining 2 factors products when they're not all constants,
// keeping sizeof() as the second factor argument.
@@
expression THING, E1, E2;
type TYPE;
constant C1, C2, C3;
@@

(
  kzalloc(sizeof(THING) * C2, ...)
|
  kzalloc(sizeof(TYPE) * C2, ...)
|
  kzalloc(C1 * C2 * C3, ...)
|
  kzalloc(C1 * C2, ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(TYPE) * (E2)
+	E2, sizeof(TYPE)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(TYPE) * E2
+	E2, sizeof(TYPE)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(THING) * (E2)
+	E2, sizeof(THING)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	sizeof(THING) * E2
+	E2, sizeof(THING)
  , ...)
|
- kzalloc
+ kcalloc
  (
-	(E1) * E2
+	E1, E2
  , ...)
|
- kzalloc
+ kcalloc
  (
-	(E1) * (E2)
+	E1, E2
  , ...)
|
- kzalloc
+ kcalloc
  (
-	E1 * E2
+	E1, E2
  , ...)
)

Signed-off-by: Kees Cook <keescook@chromium.org>
2018-06-12 16:19:22 -07:00
Kees Cook 6da2ec5605 treewide: kmalloc() -> kmalloc_array()
The kmalloc() function has a 2-factor argument form, kmalloc_array(). This
patch replaces cases of:

        kmalloc(a * b, gfp)

with:
        kmalloc_array(a * b, gfp)

as well as handling cases of:

        kmalloc(a * b * c, gfp)

with:

        kmalloc(array3_size(a, b, c), gfp)

as it's slightly less ugly than:

        kmalloc_array(array_size(a, b), c, gfp)

This does, however, attempt to ignore constant size factors like:

        kmalloc(4 * 1024, gfp)

though any constants defined via macros get caught up in the conversion.

Any factors with a sizeof() of "unsigned char", "char", and "u8" were
dropped, since they're redundant.

The tools/ directory was manually excluded, since it has its own
implementation of kmalloc().

The Coccinelle script used for this was:

// Fix redundant parens around sizeof().
@@
type TYPE;
expression THING, E;
@@

(
  kmalloc(
-	(sizeof(TYPE)) * E
+	sizeof(TYPE) * E
  , ...)
|
  kmalloc(
-	(sizeof(THING)) * E
+	sizeof(THING) * E
  , ...)
)

// Drop single-byte sizes and redundant parens.
@@
expression COUNT;
typedef u8;
typedef __u8;
@@

(
  kmalloc(
-	sizeof(u8) * (COUNT)
+	COUNT
  , ...)
|
  kmalloc(
-	sizeof(__u8) * (COUNT)
+	COUNT
  , ...)
|
  kmalloc(
-	sizeof(char) * (COUNT)
+	COUNT
  , ...)
|
  kmalloc(
-	sizeof(unsigned char) * (COUNT)
+	COUNT
  , ...)
|
  kmalloc(
-	sizeof(u8) * COUNT
+	COUNT
  , ...)
|
  kmalloc(
-	sizeof(__u8) * COUNT
+	COUNT
  , ...)
|
  kmalloc(
-	sizeof(char) * COUNT
+	COUNT
  , ...)
|
  kmalloc(
-	sizeof(unsigned char) * COUNT
+	COUNT
  , ...)
)

// 2-factor product with sizeof(type/expression) and identifier or constant.
@@
type TYPE;
expression THING;
identifier COUNT_ID;
constant COUNT_CONST;
@@

(
- kmalloc
+ kmalloc_array
  (
-	sizeof(TYPE) * (COUNT_ID)
+	COUNT_ID, sizeof(TYPE)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(TYPE) * COUNT_ID
+	COUNT_ID, sizeof(TYPE)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(TYPE) * (COUNT_CONST)
+	COUNT_CONST, sizeof(TYPE)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(TYPE) * COUNT_CONST
+	COUNT_CONST, sizeof(TYPE)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(THING) * (COUNT_ID)
+	COUNT_ID, sizeof(THING)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(THING) * COUNT_ID
+	COUNT_ID, sizeof(THING)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(THING) * (COUNT_CONST)
+	COUNT_CONST, sizeof(THING)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(THING) * COUNT_CONST
+	COUNT_CONST, sizeof(THING)
  , ...)
)

// 2-factor product, only identifiers.
@@
identifier SIZE, COUNT;
@@

- kmalloc
+ kmalloc_array
  (
-	SIZE * COUNT
+	COUNT, SIZE
  , ...)

// 3-factor product with 1 sizeof(type) or sizeof(expression), with
// redundant parens removed.
@@
expression THING;
identifier STRIDE, COUNT;
type TYPE;
@@

(
  kmalloc(
-	sizeof(TYPE) * (COUNT) * (STRIDE)
+	array3_size(COUNT, STRIDE, sizeof(TYPE))
  , ...)
|
  kmalloc(
-	sizeof(TYPE) * (COUNT) * STRIDE
+	array3_size(COUNT, STRIDE, sizeof(TYPE))
  , ...)
|
  kmalloc(
-	sizeof(TYPE) * COUNT * (STRIDE)
+	array3_size(COUNT, STRIDE, sizeof(TYPE))
  , ...)
|
  kmalloc(
-	sizeof(TYPE) * COUNT * STRIDE
+	array3_size(COUNT, STRIDE, sizeof(TYPE))
  , ...)
|
  kmalloc(
-	sizeof(THING) * (COUNT) * (STRIDE)
+	array3_size(COUNT, STRIDE, sizeof(THING))
  , ...)
|
  kmalloc(
-	sizeof(THING) * (COUNT) * STRIDE
+	array3_size(COUNT, STRIDE, sizeof(THING))
  , ...)
|
  kmalloc(
-	sizeof(THING) * COUNT * (STRIDE)
+	array3_size(COUNT, STRIDE, sizeof(THING))
  , ...)
|
  kmalloc(
-	sizeof(THING) * COUNT * STRIDE
+	array3_size(COUNT, STRIDE, sizeof(THING))
  , ...)
)

// 3-factor product with 2 sizeof(variable), with redundant parens removed.
@@
expression THING1, THING2;
identifier COUNT;
type TYPE1, TYPE2;
@@

(
  kmalloc(
-	sizeof(TYPE1) * sizeof(TYPE2) * COUNT
+	array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
  , ...)
|
  kmalloc(
-	sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+	array3_size(COUNT, sizeof(TYPE1), sizeof(TYPE2))
  , ...)
|
  kmalloc(
-	sizeof(THING1) * sizeof(THING2) * COUNT
+	array3_size(COUNT, sizeof(THING1), sizeof(THING2))
  , ...)
|
  kmalloc(
-	sizeof(THING1) * sizeof(THING2) * (COUNT)
+	array3_size(COUNT, sizeof(THING1), sizeof(THING2))
  , ...)
|
  kmalloc(
-	sizeof(TYPE1) * sizeof(THING2) * COUNT
+	array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
  , ...)
|
  kmalloc(
-	sizeof(TYPE1) * sizeof(THING2) * (COUNT)
+	array3_size(COUNT, sizeof(TYPE1), sizeof(THING2))
  , ...)
)

// 3-factor product, only identifiers, with redundant parens removed.
@@
identifier STRIDE, SIZE, COUNT;
@@

(
  kmalloc(
-	(COUNT) * STRIDE * SIZE
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kmalloc(
-	COUNT * (STRIDE) * SIZE
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kmalloc(
-	COUNT * STRIDE * (SIZE)
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kmalloc(
-	(COUNT) * (STRIDE) * SIZE
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kmalloc(
-	COUNT * (STRIDE) * (SIZE)
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kmalloc(
-	(COUNT) * STRIDE * (SIZE)
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kmalloc(
-	(COUNT) * (STRIDE) * (SIZE)
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
|
  kmalloc(
-	COUNT * STRIDE * SIZE
+	array3_size(COUNT, STRIDE, SIZE)
  , ...)
)

// Any remaining multi-factor products, first at least 3-factor products,
// when they're not all constants...
@@
expression E1, E2, E3;
constant C1, C2, C3;
@@

(
  kmalloc(C1 * C2 * C3, ...)
|
  kmalloc(
-	(E1) * E2 * E3
+	array3_size(E1, E2, E3)
  , ...)
|
  kmalloc(
-	(E1) * (E2) * E3
+	array3_size(E1, E2, E3)
  , ...)
|
  kmalloc(
-	(E1) * (E2) * (E3)
+	array3_size(E1, E2, E3)
  , ...)
|
  kmalloc(
-	E1 * E2 * E3
+	array3_size(E1, E2, E3)
  , ...)
)

// And then all remaining 2 factors products when they're not all constants,
// keeping sizeof() as the second factor argument.
@@
expression THING, E1, E2;
type TYPE;
constant C1, C2, C3;
@@

(
  kmalloc(sizeof(THING) * C2, ...)
|
  kmalloc(sizeof(TYPE) * C2, ...)
|
  kmalloc(C1 * C2 * C3, ...)
|
  kmalloc(C1 * C2, ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(TYPE) * (E2)
+	E2, sizeof(TYPE)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(TYPE) * E2
+	E2, sizeof(TYPE)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(THING) * (E2)
+	E2, sizeof(THING)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	sizeof(THING) * E2
+	E2, sizeof(THING)
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	(E1) * E2
+	E1, E2
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	(E1) * (E2)
+	E1, E2
  , ...)
|
- kmalloc
+ kmalloc_array
  (
-	E1 * E2
+	E1, E2
  , ...)
)

Signed-off-by: Kees Cook <keescook@chromium.org>
2018-06-12 16:19:22 -07:00
Linus Torvalds 92400b8c8b Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:

 - Lots of tidying up changes all across the map for Linux's formal
   memory/locking-model tooling, by Alan Stern, Akira Yokosawa, Andrea
   Parri, Paul E. McKenney and SeongJae Park.

   Notable changes beyond an overall update in the tooling itself is the
   tidying up of spin_is_locked() semantics, which spills over into the
   kernel proper as well.

 - qspinlock improvements: the locking algorithm now guarantees forward
   progress whereas the previous implementation in mainline could starve
   threads indefinitely in cmpxchg() loops. Also other related cleanups
   to the qspinlock code (Will Deacon)

 - misc smaller improvements, cleanups and fixes all across the locking
   subsystem

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (51 commits)
  locking/rwsem: Simplify the is-owner-spinnable checks
  tools/memory-model: Add reference for 'Simplifying ARM concurrency'
  tools/memory-model: Update ASPLOS information
  MAINTAINERS, tools/memory-model: Update e-mail address for Andrea Parri
  tools/memory-model: Fix coding style in 'lock.cat'
  tools/memory-model: Remove out-of-date comments and code from lock.cat
  tools/memory-model: Improve mixed-access checking in lock.cat
  tools/memory-model: Improve comments in lock.cat
  tools/memory-model: Remove duplicated code from lock.cat
  tools/memory-model: Flag "cumulativity" and "propagation" tests
  tools/memory-model: Add model support for spin_is_locked()
  tools/memory-model: Add scripts to test memory model
  tools/memory-model: Fix coding style in 'linux-kernel.def'
  tools/memory-model: Model 'smp_store_mb()'
  tools/memory-order: Update the cheat-sheet to show that smp_mb__after_atomic() orders later RMW operations
  tools/memory-order: Improve key for SELF and SV
  tools/memory-model: Fix cheat sheet typo
  tools/memory-model: Update required version of herdtools7
  tools/memory-model: Redefine rb in terms of rcu-fence
  tools/memory-model: Rename link and rcu-path to rcu-link and rb
  ...
2018-06-04 16:40:11 -07:00
Linus Torvalds cf626b0da7 Merge branch 'hch.procfs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull procfs updates from Al Viro:
 "Christoph's proc_create_... cleanups series"

* 'hch.procfs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (44 commits)
  xfs, proc: hide unused xfs procfs helpers
  isdn/gigaset: add back gigaset_procinfo assignment
  proc: update SIZEOF_PDE_INLINE_NAME for the new pde fields
  tty: replace ->proc_fops with ->proc_show
  ide: replace ->proc_fops with ->proc_show
  ide: remove ide_driver_proc_write
  isdn: replace ->proc_fops with ->proc_show
  atm: switch to proc_create_seq_private
  atm: simplify procfs code
  bluetooth: switch to proc_create_seq_data
  netfilter/x_tables: switch to proc_create_seq_private
  netfilter/xt_hashlimit: switch to proc_create_{seq,single}_data
  neigh: switch to proc_create_seq_data
  hostap: switch to proc_create_{seq,single}_data
  bonding: switch to proc_create_seq_data
  rtc/proc: switch to proc_create_single_data
  drbd: switch to proc_create_single
  resource: switch to proc_create_seq_data
  staging/rtl8192u: simplify procfs code
  jfs: simplify procfs code
  ...
2018-06-04 10:00:01 -07:00
Oleg Nesterov 1b22fc609c locking/rwsem: Simplify the is-owner-spinnable checks
Add the trivial owner_on_cpu() helper for rwsem_can_spin_on_owner() and
rwsem_spin_on_owner(), it also allows to make rwsem_can_spin_on_owner()
a bit more clear.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180518165534.GA22348@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-25 08:11:47 +02:00
Ingo Molnar 675c00c332 Merge branch 'linus' into locking/core, to pick up fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-25 08:11:28 +02:00
Waiman Long 5a817641f6 locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN
The filesystem freezing code needs to transfer ownership of a rwsem
embedded in a percpu-rwsem from the task that does the freezing to
another one that does the thawing by calling percpu_rwsem_release()
after freezing and percpu_rwsem_acquire() before thawing.

However, the new rwsem debug code runs afoul with this scheme by warning
that the task that releases the rwsem isn't the one that acquires it,
as reported by Amir Goldstein:

  DEBUG_LOCKS_WARN_ON(sem->owner != get_current())
  WARNING: CPU: 1 PID: 1401 at /home/amir/build/src/linux/kernel/locking/rwsem.c:133 up_write+0x59/0x79

  Call Trace:
   percpu_up_write+0x1f/0x28
   thaw_super_locked+0xdf/0x120
   do_vfs_ioctl+0x270/0x5f1
   ksys_ioctl+0x52/0x71
   __x64_sys_ioctl+0x16/0x19
   do_syscall_64+0x5d/0x167
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

To work properly with the rwsem debug code, we need to annotate that the
rwsem ownership is unknown during the tranfer period until a brave soul
comes forward to acquire the ownership. During that period, optimistic
spinning will be disabled.

Reported-by: Amir Goldstein <amir73il@gmail.com>
Tested-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-fsdevel@vger.kernel.org
Link: http://lkml.kernel.org/r/1526420991-21213-3-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-16 11:45:16 +02:00
Waiman Long d7d760efad locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED flag
There are use cases where a rwsem can be acquired by one task, but
released by another task. In thess cases, optimistic spinning may need
to be disabled.  One example will be the filesystem freeze/thaw code
where the task that freezes the filesystem will acquire a write lock
on a rwsem and then un-owns it before returning to userspace. Later on,
another task will come along, acquire the ownership, thaw the filesystem
and release the rwsem.

Bit 0 of the owner field was used to designate that it is a reader
owned rwsem. It is now repurposed to mean that the owner of the rwsem
is not known. If only bit 0 is set, the rwsem is reader owned. If bit
0 and other bits are set, it is writer owned with an unknown owner.
One such value for the latter case is (-1L). So we can set owner to 1 for
reader-owned, -1 for writer-owned. The owner is unknown in both cases.

To handle transfer of rwsem ownership, the higher level code should
set the owner field to -1 to indicate a write-locked rwsem with unknown
owner.  Optimistic spinning will be disabled in this case.

Once the higher level code figures who the new owner is, it can then
set the owner field accordingly.

Tested-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-fsdevel@vger.kernel.org
Link: http://lkml.kernel.org/r/1526420991-21213-2-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-16 11:45:15 +02:00
Christoph Hellwig 3f3942aca6 proc: introduce proc_create_single{,_data}
Variants of proc_create{,_data} that directly take a seq_file show
callback and drastically reduces the boilerplate code in the callers.

All trivial callers converted over.

Signed-off-by: Christoph Hellwig <hch@lst.de>
2018-05-16 07:23:35 +02:00
Christoph Hellwig fddda2b7b5 proc: introduce proc_create_seq{,_data}
Variants of proc_create{,_data} that directly take a struct seq_operations
argument and drastically reduces the boilerplate code in the callers.

All trivial callers converted over.

Signed-off-by: Christoph Hellwig <hch@lst.de>
2018-05-16 07:23:35 +02:00
Tetsuo Handa 8cc05c71ba locking/lockdep: Move sanity check to inside lockdep_print_held_locks()
Calling lockdep_print_held_locks() on a running thread is considered unsafe.

Since all callers should follow that rule and the sanity check is not heavy,
this patch moves the sanity check to inside lockdep_print_held_locks().

As a side effect of this patch, the number of locks held by running threads
will be printed as well. This change will be preferable when we want to
know which threads might be relevant to a problem but are unable to print
any clues because that thread is running.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1523011279-8206-2-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-14 09:15:02 +02:00
Tetsuo Handa 0f736a52e4 locking/lockdep: Use for_each_process_thread() for debug_show_all_locks()
debug_show_all_locks() tries to grab the tasklist_lock for two seconds, but
calling while_each_thread() without tasklist_lock held is not safe.

See the following commit for more information:

  4449a51a7c ("vm_is_stack: use for_each_thread() rather then buggy while_each_thread()")

Change debug_show_all_locks() from "do_each_thread()/while_each_thread()
with possibility of missing tasklist_lock" to "for_each_process_thread()
with RCU", and add a call to touch_all_softlockup_watchdogs() like
show_state_filter() does.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1523011279-8206-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-14 09:15:02 +02:00
Peter Zijlstra c427f69564 locking/mutex: Optimize __mutex_trylock_fast()
Use try_cmpxchg to avoid the pointless TEST instruction..
And add the (missing) atomic_long_try_cmpxchg*() wrappery.

On x86_64 this gives:

0000000000000710 <mutex_lock>:						0000000000000710 <mutex_lock>:
 710:   65 48 8b 14 25 00 00    mov    %gs:0x0,%rdx                      710:   65 48 8b 14 25 00 00    mov    %gs:0x0,%rdx
 717:   00 00                                                            717:   00 00
                        715: R_X86_64_32S       current_task                                    715: R_X86_64_32S       current_task
 719:   31 c0                   xor    %eax,%eax                         719:   31 c0                   xor    %eax,%eax
 71b:   f0 48 0f b1 17          lock cmpxchg %rdx,(%rdi)                 71b:   f0 48 0f b1 17          lock cmpxchg %rdx,(%rdi)
 720:   48 85 c0                test   %rax,%rax                         720:   75 02                   jne    724 <mutex_lock+0x14>
 723:   75 02                   jne    727 <mutex_lock+0x17>             722:   f3 c3                   repz retq
 725:   f3 c3                   repz retq                                724:   eb da                   jmp    700 <__mutex_lock_slowpath>
 727:   eb d7                   jmp    700 <__mutex_lock_slowpath>       726:   66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
 729:   0f 1f 80 00 00 00 00    nopl   0x0(%rax)                         72d:   00 00 00

On ARM64 this gives:

000000000000638 <mutex_lock>:						0000000000000638 <mutex_lock>:
     638:       d5384101        mrs     x1, sp_el0                           638:       d5384101        mrs     x1, sp_el0
     63c:       d2800002        mov     x2, #0x0                             63c:       d2800002        mov     x2, #0x0
     640:       f9800011        prfm    pstl1strm, [x0]                      640:       f9800011        prfm    pstl1strm, [x0]
     644:       c85ffc03        ldaxr   x3, [x0]                             644:       c85ffc03        ldaxr   x3, [x0]
     648:       ca020064        eor     x4, x3, x2                           648:       ca020064        eor     x4, x3, x2
     64c:       b5000064        cbnz    x4, 658 <mutex_lock+0x20>            64c:       b5000064        cbnz    x4, 658 <mutex_lock+0x20>
     650:       c8047c01        stxr    w4, x1, [x0]                         650:       c8047c01        stxr    w4, x1, [x0]
     654:       35ffff84        cbnz    w4, 644 <mutex_lock+0xc>             654:       35ffff84        cbnz    w4, 644 <mutex_lock+0xc>
     658:       b40000c3        cbz     x3, 670 <mutex_lock+0x38>            658:       b5000043        cbnz    x3, 660 <mutex_lock+0x28>
     65c:       a9bf7bfd        stp     x29, x30, [sp,#-16]!                 65c:       d65f03c0        ret
     660:       910003fd        mov     x29, sp                              660:       a9bf7bfd        stp     x29, x30, [sp,#-16]!
     664:       97ffffef        bl      620 <__mutex_lock_slowpath>          664:       910003fd        mov     x29, sp
     668:       a8c17bfd        ldp     x29, x30, [sp],#16                   668:       97ffffee        bl      620 <__mutex_lock_slowpath>
     66c:       d65f03c0        ret                                          66c:       a8c17bfd        ldp     x29, x30, [sp],#16
     670:       d65f03c0        ret                                          670:       d65f03c0        ret

Reported-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-04 10:02:39 +02:00
Will Deacon 3bea9adc96 locking/qspinlock: Remove duplicate clear_pending() function from PV code
The native clear_pending() function is identical to the PV version, so the
latter can simply be removed.

This fixes the build for systems with >= 16K CPUs using the PV lock implementation.

Reported-by: Waiman Long <longman@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20180427101619.GB21705@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 12:55:22 +02:00
Waiman Long 81d3dc9a34 locking/qspinlock: Add stat tracking for pending vs. slowpath
Currently, the qspinlock_stat code tracks only statistical counts in the
PV qspinlock code. However, it may also be useful to track the number
of locking operations done via the pending code vs. the MCS lock queue
slowpath for the non-PV case.

The qspinlock stat code is modified to do that. The stat counter
pv_lock_slowpath is renamed to lock_slowpath so that it can be used by
both the PV and non-PV cases.

Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1524738868-31318-14-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:53 +02:00
Will Deacon ae75d9089f locking/qspinlock: Use try_cmpxchg() instead of cmpxchg() when locking
When reaching the head of an uncontended queue on the qspinlock slow-path,
using a try_cmpxchg() instead of a cmpxchg() operation to transition the
lock work to _Q_LOCKED_VAL generates slightly better code for x86 and
pretty much identical code for arm64.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-13-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:52 +02:00
Will Deacon 9d4646d14d locking/qspinlock: Elide back-to-back RELEASE operations with smp_wmb()
The qspinlock slowpath must ensure that the MCS node is fully initialised
before it can be reached by another other CPU. This is currently enforced
by using a RELEASE operation when updating the tail and also when linking
the node into the waitqueue, since the control dependency off xchg_tail
is insufficient to enforce sufficient ordering, see:

  95bcade33a ("locking/qspinlock: Ensure node is initialised before updating prev->next")

Back-to-back RELEASE operations may be expensive on some architectures,
particularly those that implement them using fences under the hood. We
can replace the two RELEASE operations with a single smp_wmb() fence and
use RELAXED operations for the subsequent publishing of the node.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-12-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:52 +02:00
Will Deacon c131a198c4 locking/qspinlock: Use smp_cond_load_relaxed() to wait for next node
When a locker reaches the head of the queue and takes the lock, a
concurrent locker may enqueue and force the lock holder to spin
whilst its node->next field is initialised. Rather than open-code
a READ_ONCE/cpu_relax() loop, this can be implemented using
smp_cond_load_relaxed() instead.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-10-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:50 +02:00
Jason Low 7f56b58a92 locking/mcs: Use smp_cond_load_acquire() in MCS spin loop
For qspinlocks on ARM64, we would like to use WFE instead
of purely spinning. Qspinlocks internally have lock
contenders spin on an MCS lock.

Update arch_mcs_spin_lock_contended() such that it uses
the new smp_cond_load_acquire() so that ARM64 can also
override this spin loop with its own implementation using WFE.

On x86, this can also be cheaper than spinning on
smp_load_acquire().

Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-9-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:49 +02:00
Will Deacon f9c811fac4 locking/qspinlock: Use atomic_cond_read_acquire()
Rather than dig into the counter field of the atomic_t inside the
qspinlock structure so that we can call smp_cond_load_acquire(), use
atomic_cond_read_acquire() instead, which operates on the atomic_t
directly.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-8-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:49 +02:00
Will Deacon c61da58d8a locking/qspinlock: Kill cmpxchg() loop when claiming lock from head of queue
When a queued locker reaches the head of the queue, it claims the lock
by setting _Q_LOCKED_VAL in the lockword. If there isn't contention, it
must also clear the tail as part of this operation so that subsequent
lockers can avoid taking the slowpath altogether.

Currently this is expressed as a cmpxchg() loop that practically only
runs up to two iterations. This is confusing to the reader and unhelpful
to the compiler. Rewrite the cmpxchg() loop without the loop, so that a
failed cmpxchg() implies that there is contention and we just need to
write to _Q_LOCKED_VAL without considering the rest of the lockword.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-7-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:48 +02:00
Will Deacon 59fb586b4a locking/qspinlock: Remove unbounded cmpxchg() loop from locking slowpath
The qspinlock locking slowpath utilises a "pending" bit as a simple form
of an embedded test-and-set lock that can avoid the overhead of explicit
queuing in cases where the lock is held but uncontended. This bit is
managed using a cmpxchg() loop which tries to transition the uncontended
lock word from (0,0,0) -> (0,0,1) or (0,0,1) -> (0,1,1).

Unfortunately, the cmpxchg() loop is unbounded and lockers can be starved
indefinitely if the lock word is seen to oscillate between unlocked
(0,0,0) and locked (0,0,1). This could happen if concurrent lockers are
able to take the lock in the cmpxchg() loop without queuing and pass it
around amongst themselves.

This patch fixes the problem by unconditionally setting _Q_PENDING_VAL
using atomic_fetch_or, and then inspecting the old value to see whether
we need to spin on the current lock owner, or whether we now effectively
hold the lock. The tricky scenario is when concurrent lockers end up
queuing on the lock and the lock becomes available, causing us to see
a lockword of (n,0,0). With pending now set, simply queuing could lead
to deadlock as the head of the queue may not have observed the pending
flag being cleared. Conversely, if the head of the queue did observe
pending being cleared, then it could transition the lock from (n,0,0) ->
(0,0,1) meaning that any attempt to "undo" our setting of the pending
bit could race with a concurrent locker trying to set it.

We handle this race by preserving the pending bit when taking the lock
after reaching the head of the queue and leaving the tail entry intact
if we saw pending set, because we know that the tail is going to be
updated shortly.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-6-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:47 +02:00
Will Deacon 6512276d97 locking/qspinlock: Bound spinning on pending->locked transition in slowpath
If a locker taking the qspinlock slowpath reads a lock value indicating
that only the pending bit is set, then it will spin whilst the
concurrent pending->locked transition takes effect.

Unfortunately, there is no guarantee that such a transition will ever be
observed since concurrent lockers could continuously set pending and
hand over the lock amongst themselves, leading to starvation. Whilst
this would probably resolve in practice, it means that it is not
possible to prove liveness properties about the lock and means that lock
acquisition time is unbounded.

Rather than removing the pending->locked spinning from the slowpath
altogether (which has been shown to heavily penalise a 2-threaded
locking stress test on x86), this patch replaces the explicit spinning
with a call to atomic_cond_read_relaxed and allows the architecture to
provide a bound on the number of spins. For architectures that can
respond to changes in cacheline state in their smp_cond_load implementation,
it should be sufficient to use the default bound of 1.

Suggested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-4-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:46 +02:00
Will Deacon 625e88be1f locking/qspinlock: Merge 'struct __qspinlock' into 'struct qspinlock'
'struct __qspinlock' provides a handy union of fields so that
subcomponents of the lockword can be accessed by name, without having to
manage shifts and masks explicitly and take endianness into account.

This is useful in qspinlock.h and also potentially in arch headers, so
move the 'struct __qspinlock' into 'struct qspinlock' and kill the extra
definition.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-3-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-04-27 09:48:45 +02:00
Waiman Long 5149cbac42 locking/rwsem: Add DEBUG_RWSEMS to look for lock/unlock mismatches
For a rwsem, locking can either be exclusive or shared. The corresponding
exclusive or shared unlock must be used. Otherwise, the protected data
structures may get corrupted or the lock may be in an inconsistent state.

In order to detect such anomaly, a new configuration option DEBUG_RWSEMS
is added which can be enabled to look for such mismatches and print
warnings that that happens.

Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1522445280-7767-2-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-31 07:30:50 +02:00
Ingo Molnar 169310f71f Merge branch 'linus' into locking/core, to pick up fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-31 07:30:17 +02:00
Tetsuo Handa b3c39758c8 lockdep: Make the lock debug output more useful
The lock debug output in print_lock() has a few shortcomings:

 - It prints the hlock->acquire_ip field in %px and %pS format. That's
   redundant information.

 - It lacks information about the lock object itself. The lock class is
   not helpful to identify a particular instance of a lock.

Change the output so it prints:

 - hlock->instance to allow identification of a particular lock instance.

 - only the %pS format of hlock->ip_acquire which is sufficient to decode
   the actual code line with faddr2line.

The resulting output is:

3 locks held by a.out/31106:
#0: 00000000b0f753ba (&mm->mmap_sem){++++}, at: copy_process.part.41+0x10d5/0x1fe0
#1: 00000000ef64d539 (&mm->mmap_sem/1){+.+.}, at: copy_process.part.41+0x10fe/0x1fe0
#2: 00000000b41a282e (&mapping->i_mmap_rwsem){++++}, at: copy_process.part.41+0x12f2/0x1fe0

[ tglx: Massaged changelog ]

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: linux-mm@kvack.org
Cc: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/201803271941.GBE57310.tVSOJLQOFFOHFM@I-love.SAKURA.ne.jp
2018-03-29 14:41:40 +02:00
Peter Zijlstra c28d62cf52 locking/rtmutex: Handle non enqueued waiters gracefully in remove_waiter()
In -RT task_blocks_on_rt_mutex() may return with -EAGAIN due to
(->pi_blocked_on == PI_WAKEUP_INPROGRESS) before it added itself as a
waiter. In such a case remove_waiter() must not be called because without a
waiter it will trigger the BUG_ON() statement.

This was initially reported by Yimin Deng. Thomas Gleixner fixed it then
with an explicit check for waiters before calling remove_waiter().

Instead of an explicit NULL check before calling rt_mutex_top_waiter() make
the function return NULL if there are no waiters. With that fixed the now
pointless NULL check is removed from rt_mutex_slowlock().

Reported-and-debugged-by: Yimin Deng <yimin11.deng@gmail.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/CAAh1qt=DCL9aUXNxanP5BKtiPp3m+qj4yB+gDohhXPVFCxWwzg@mail.gmail.com
Link: https://lkml.kernel.org/r/20180327121438.sss7hxg3crqy4ecd@linutronix.de
2018-03-28 23:01:30 +02:00
Matthew Wilcox 45dbac0e28 locking/mutex: Improve documentation
On Wed, Mar 14, 2018 at 01:56:31PM -0700, Andrew Morton wrote:

> My memory is weak and our documentation is awful.  What does
> mutex_lock_killable() actually do and how does it differ from
> mutex_lock_interruptible()?

Add kernel-doc for mutex_lock_killable() and mutex_lock_io().  Reword the
kernel-doc for mutex_lock_interruptible().

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: cl@linux.com
Cc: tj@kernel.org
Link: http://lkml.kernel.org/r/20180315115812.GA9949@bombadil.infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-20 08:07:41 +01:00
Ingo Molnar 9884afa2fd Linux 4.16-rc5
-----BEGIN PGP SIGNATURE-----
 
 iQFSBAABCAA8FiEEq68RxlopcLEwq+PEeb4+QwBBGIYFAlqlyPEeHHRvcnZhbGRz
 QGxpbnV4LWZvdW5kYXRpb24ub3JnAAoJEHm+PkMAQRiGNa0H/RIa/StQuYu/SBwa
 JRqQFmkIsx+gG+FyamJrqGzRfyjounES8PbfyaN3cCrzYgeRwMp1U/bZW6/l5tkb
 OjTtrCJ6CJaa21fC/7aqn3rhejHciKyk83EinMu5WjDpsQcaF2xKr3SaPa62Ja24
 fhawKq3CnUa+OUuAbicVX8yn4viUB6x8FjSN/IWfp3Cs4IBR7SGxxD7A4MET9FbQ
 5OOu0al8ly9QeCggTtJyk+cApeLfexEBTbUur9gm7GcH9jhUtJSyZCZsDJx6M2yb
 CwdgF4fyk58c1fuHvTFb0AdUns55ba3nicybRHHMVbDpZIG9v4/M1yJETHHf5cD7
 t3rFjrY=
 =+Ldf
 -----END PGP SIGNATURE-----

Merge tag 'v4.16-rc5' into locking/core, to pick up fixes

Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-12 12:14:57 +01:00
Boqun Feng 6b0ef92fee rtmutex: Make rt_mutex_futex_unlock() safe for irq-off callsites
When running rcutorture with TREE03 config, CONFIG_PROVE_LOCKING=y, and
kernel cmdline argument "rcutorture.gp_exp=1", lockdep reports a
HARDIRQ-safe->HARDIRQ-unsafe deadlock:

 ================================
 WARNING: inconsistent lock state
 4.16.0-rc4+ #1 Not tainted
 --------------------------------
 inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.
 takes:
 __schedule+0xbe/0xaf0
 {IN-HARDIRQ-W} state was registered at:
   _raw_spin_lock+0x2a/0x40
   scheduler_tick+0x47/0xf0
...
 other info that might help us debug this:
  Possible unsafe locking scenario:
        CPU0
        ----
   lock(&rq->lock);
   <Interrupt>
     lock(&rq->lock);
  *** DEADLOCK ***
 1 lock held by rcu_torture_rea/724:
 rcu_torture_read_lock+0x0/0x70
 stack backtrace:
 CPU: 2 PID: 724 Comm: rcu_torture_rea Not tainted 4.16.0-rc4+ #1
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014
 Call Trace:
  lock_acquire+0x90/0x200
  ? __schedule+0xbe/0xaf0
  _raw_spin_lock+0x2a/0x40
  ? __schedule+0xbe/0xaf0
  __schedule+0xbe/0xaf0
  preempt_schedule_irq+0x2f/0x60
  retint_kernel+0x1b/0x2d
 RIP: 0010:rcu_read_unlock_special+0x0/0x680
  ? rcu_torture_read_unlock+0x60/0x60
  __rcu_read_unlock+0x64/0x70
  rcu_torture_read_unlock+0x17/0x60
  rcu_torture_reader+0x275/0x450
  ? rcutorture_booster_init+0x110/0x110
  ? rcu_torture_stall+0x230/0x230
  ? kthread+0x10e/0x130
  kthread+0x10e/0x130
  ? kthread_create_worker_on_cpu+0x70/0x70
  ? call_usermodehelper_exec_async+0x11a/0x150
  ret_from_fork+0x3a/0x50

This happens with the following even sequence:

	preempt_schedule_irq();
	  local_irq_enable();
	  __schedule():
	    local_irq_disable(); // irq off
	    ...
	    rcu_note_context_switch():
	      rcu_note_preempt_context_switch():
	        rcu_read_unlock_special():
	          local_irq_save(flags);
	          ...
		  raw_spin_unlock_irqrestore(...,flags); // irq remains off
	          rt_mutex_futex_unlock():
	            raw_spin_lock_irq();
	            ...
	            raw_spin_unlock_irq(); // accidentally set irq on

	    <return to __schedule()>
	    rq_lock():
	      raw_spin_lock(); // acquiring rq->lock with irq on

which means rq->lock becomes a HARDIRQ-unsafe lock, which can cause
deadlocks in scheduler code.

This problem was introduced by commit 02a7c234e5 ("rcu: Suppress
lockdep false-positive ->boost_mtx complaints"). That brought the user
of rt_mutex_futex_unlock() with irq off.

To fix this, replace the *lock_irq() in rt_mutex_futex_unlock() with
*lock_irq{save,restore}() to make it safe to call rt_mutex_futex_unlock()
with irq off.

Fixes: 02a7c234e5 ("rcu: Suppress lockdep false-positive ->boost_mtx complaints")
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>
Link: https://lkml.kernel.org/r/20180309065630.8283-1-boqun.feng@gmail.com
2018-03-09 11:06:16 +01:00
Borislav Petkov 04860d48a8 locking/lockdep: Show unadorned pointers
Show unadorned pointers in lockdep reports - lockdep is a debugging
facility and hashing pointers there doesn't make a whole lotta sense.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20180226134926.23069-1-bp@alien8.de
2018-02-28 15:25:44 +01:00
Will Deacon 11dc13224c locking/qspinlock: Ensure node->count is updated before initialising node
When queuing on the qspinlock, the count field for the current CPU's head
node is incremented. This needn't be atomic because locking in e.g. IRQ
context is balanced and so an IRQ will return with node->count as it
found it.

However, the compiler could in theory reorder the initialisation of
node[idx] before the increment of the head node->count, causing an
IRQ to overwrite the initialised node and potentially corrupt the lock
state.

Avoid the potential for this harmful compiler reordering by placing a
barrier() between the increment of the head node->count and the subsequent
node initialisation.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1518528177-19169-3-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-13 14:50:14 +01:00
Will Deacon 95bcade33a locking/qspinlock: Ensure node is initialised before updating prev->next
When a locker ends up queuing on the qspinlock locking slowpath, we
initialise the relevant mcs node and publish it indirectly by updating
the tail portion of the lock word using xchg_tail. If we find that there
was a pre-existing locker in the queue, we subsequently update their
->next field to point at our node so that we are notified when it's our
turn to take the lock.

This can be roughly illustrated as follows:

  /* Initialise the fields in node and encode a pointer to node in tail */
  tail = initialise_node(node);

  /*
   * Exchange tail into the lockword using an atomic read-modify-write
   * operation with release semantics
   */
  old = xchg_tail(lock, tail);

  /* If there was a pre-existing waiter ... */
  if (old & _Q_TAIL_MASK) {
	prev = decode_tail(old);
	smp_read_barrier_depends();

	/* ... then update their ->next field to point to node.
	WRITE_ONCE(prev->next, node);
  }

The conditional update of prev->next therefore relies on the address
dependency from the result of xchg_tail ensuring order against the
prior initialisation of node. However, since the release semantics of
the xchg_tail operation apply only to the write portion of the RmW,
then this ordering is not guaranteed and it is possible for the CPU
to return old before the writes to node have been published, consequently
allowing us to point prev->next to an uninitialised node.

This patch fixes the problem by making the update of prev->next a RELEASE
operation, which also removes the reliance on dependency ordering.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1518528177-19169-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-13 14:50:14 +01:00