Commit Graph

117 Commits

Author SHA1 Message Date
Linus Torvalds 8e9a2dba86 Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull core locking updates from Ingo Molnar:
 "The main changes in this cycle are:

   - Another attempt at enabling cross-release lockdep dependency
     tracking (automatically part of CONFIG_PROVE_LOCKING=y), this time
     with better performance and fewer false positives. (Byungchul Park)

   - Introduce lockdep_assert_irqs_enabled()/disabled() and convert
     open-coded equivalents to lockdep variants. (Frederic Weisbecker)

   - Add down_read_killable() and use it in the VFS's iterate_dir()
     method. (Kirill Tkhai)

   - Convert remaining uses of ACCESS_ONCE() to
     READ_ONCE()/WRITE_ONCE(). Most of the conversion was Coccinelle
     driven. (Mark Rutland, Paul E. McKenney)

   - Get rid of lockless_dereference(), by strengthening Alpha atomics,
     strengthening READ_ONCE() with smp_read_barrier_depends() and thus
     being able to convert users of lockless_dereference() to
     READ_ONCE(). (Will Deacon)

   - Various micro-optimizations:

        - better PV qspinlocks (Waiman Long),
        - better x86 barriers (Michael S. Tsirkin)
        - better x86 refcounts (Kees Cook)

   - ... plus other fixes and enhancements. (Borislav Petkov, Juergen
     Gross, Miguel Bernal Marin)"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (70 commits)
  locking/x86: Use LOCK ADD for smp_mb() instead of MFENCE
  rcu: Use lockdep to assert IRQs are disabled/enabled
  netpoll: Use lockdep to assert IRQs are disabled/enabled
  timers/posix-cpu-timers: Use lockdep to assert IRQs are disabled/enabled
  sched/clock, sched/cputime: Use lockdep to assert IRQs are disabled/enabled
  irq_work: Use lockdep to assert IRQs are disabled/enabled
  irq/timings: Use lockdep to assert IRQs are disabled/enabled
  perf/core: Use lockdep to assert IRQs are disabled/enabled
  x86: Use lockdep to assert IRQs are disabled/enabled
  smp/core: Use lockdep to assert IRQs are disabled/enabled
  timers/hrtimer: Use lockdep to assert IRQs are disabled/enabled
  timers/nohz: Use lockdep to assert IRQs are disabled/enabled
  workqueue: Use lockdep to assert IRQs are disabled/enabled
  irq/softirqs: Use lockdep to assert IRQs are disabled/enabled
  locking/lockdep: Add IRQs disabled/enabled assertion APIs: lockdep_assert_irqs_enabled()/disabled()
  locking/pvqspinlock: Implement hybrid PV queued/unfair locks
  locking/rwlocks: Fix comments
  x86/paravirt: Set up the virt_spin_lock_key after static keys get initialized
  block, locking/lockdep: Assign a lock_class per gendisk used for wait_for_completion()
  workqueue: Remove now redundant lock acquisitions wrt. workqueue flushes
  ...
2017-11-13 12:38:26 -08:00
Will Deacon 59ecbbe7b3 locking/barriers: Kill lockless_dereference()
lockless_dereference() is a nice idea, but it gained little traction in
kernel code since its introduction three years ago. This is partly
because it's a pain to type, but also because using READ_ONCE() instead
has worked correctly on all architectures apart from Alpha, which is a
fully supported but somewhat niche architecture these days.

Now that READ_ONCE() has been upgraded to contain an implicit
smp_read_barrier_depends() and the few callers of lockless_dereference()
have been converted, we can remove lockless_dereference() altogether.

Signed-off-by: Will Deacon <will.deacon@arm.com>
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/1508840570-22169-5-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-24 13:17:33 +02:00
Guilherme G. Piccoli 5692fcc671 doc: Rewrite confusing statement about memory barriers
The "Write (or store) memory barriers" bullet of the "Variety of memory
barriers" section, calls out a sequential order of stores, which is
confusing since sequential ordering is not guaranteed.

This commit therefore rewords to avoid mentioning a sequence of stores
to clarify the intent.

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-20 11:09:32 -07:00
Scott Tsai d92f842bb3 memory-barriers.txt: Fix typo in pairing example
In the "general barrier pairing with implicit control depdendency"
example, the last write by CPU 1 was meant to change variable x and not
y. The example would be pretty uninteresting if no CPU ever changes x
and the variable was initialized to zero.

Signed-off-by: Scott Tsai <scottt@scottt.tw>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-20 11:09:32 -07:00
Alan Stern 0902b1f44a memory-barriers: Rework multicopy-atomicity section
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-09 14:23:37 -07:00
Paul E. McKenney f1ab25a30c memory-barriers: Replace uses of "transitive"
The current version of memory-barriers.txt misuses the term "transitive",
so this commit replaces it with multi-copy atomic, also adding a
definition of this term.

Reported-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-09 14:23:36 -07:00
Linus Torvalds 5f82e71a00 Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:

 - Add 'cross-release' support to lockdep, which allows APIs like
   completions, where it's not the 'owner' who releases the lock, to be
   tracked. It's all activated automatically under
   CONFIG_PROVE_LOCKING=y.

 - Clean up (restructure) the x86 atomics op implementation to be more
   readable, in preparation of KASAN annotations. (Dmitry Vyukov)

 - Fix static keys (Paolo Bonzini)

 - Add killable versions of down_read() et al (Kirill Tkhai)

 - Rework and fix jump_label locking (Marc Zyngier, Paolo Bonzini)

 - Rework (and fix) tlb_flush_pending() barriers (Peter Zijlstra)

 - Remove smp_mb__before_spinlock() and convert its usages, introduce
   smp_mb__after_spinlock() (Peter Zijlstra)

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (56 commits)
  locking/lockdep/selftests: Fix mixed read-write ABBA tests
  sched/completion: Avoid unnecessary stack allocation for COMPLETION_INITIALIZER_ONSTACK()
  acpi/nfit: Fix COMPLETION_INITIALIZER_ONSTACK() abuse
  locking/pvqspinlock: Relax cmpxchg's to improve performance on some architectures
  smp: Avoid using two cache lines for struct call_single_data
  locking/lockdep: Untangle xhlock history save/restore from task independence
  locking/refcounts, x86/asm: Disable CONFIG_ARCH_HAS_REFCOUNT for the time being
  futex: Remove duplicated code and fix undefined behaviour
  Documentation/locking/atomic: Finish the document...
  locking/lockdep: Fix workqueue crossrelease annotation
  workqueue/lockdep: 'Fix' flush_work() annotation
  locking/lockdep/selftests: Add mixed read-write ABBA tests
  mm, locking/barriers: Clarify tlb_flush_pending() barriers
  locking/lockdep: Make CONFIG_LOCKDEP_CROSSRELEASE and CONFIG_LOCKDEP_COMPLETIONS truly non-interactive
  locking/lockdep: Explicitly initialize wq_barrier::done::map
  locking/lockdep: Rename CONFIG_LOCKDEP_COMPLETE to CONFIG_LOCKDEP_COMPLETIONS
  locking/lockdep: Reword title of LOCKDEP_CROSSRELEASE config
  locking/lockdep: Make CONFIG_LOCKDEP_CROSSRELEASE part of CONFIG_PROVE_LOCKING
  locking/refcounts, x86/asm: Implement fast refcount overflow protection
  locking/lockdep: Fix the rollback and overwrite detection logic in crossrelease
  ...
2017-09-04 11:52:29 -07:00
Paul E. McKenney 66ce3a4dcb doc: Update memory-barriers.txt for read-to-write dependencies
The memory-barriers.txt document contains an obsolete passage stating that
smp_read_barrier_depends() is required to force ordering for read-to-write
dependencies.  We now know that this is not required, even for DEC Alpha.
This commit therefore updates this passage to state that read-to-write
dependencies are respected even without smp_read_barrier_depends().

Reported-by: Lance Roy <ldr709@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Luc Maranget <luc.maranget@inria.fr>
[ paulmck: Reference control-dependencies sections and use WRITE_ONCE()
  per Will Deacon.  Correctly place split-cache paragraph while there. ]
Acked-by: Will Deacon <will.deacon@arm.com>
2017-08-17 07:29:57 -07:00
Peter Zijlstra a9668cd6ee locking: Remove smp_mb__before_spinlock()
Now that there are no users of smp_mb__before_spinlock() left, remove
it entirely.

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>
2017-08-10 12:29:03 +02:00
Peter Zijlstra 706eeb3e9c Documentation/locking/atomic: Add documents for new atomic_t APIs
Since we've vastly expanded the atomic_t interface in recent years the
existing documentation is woefully out of date and people seem to get
confused a bit.

Start a new document to hopefully better explain the current state of
affairs.

The old atomic_ops.txt also covers bitmaps and a few more details so
this is not a full replacement and we'll therefore keep that document
around until such a time that we've managed to write more text to cover
its entire.

Also please, ReST people, go away.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-08-10 12:29:00 +02:00
Linus Torvalds 954e6e03c6 A set of fixes for various warnings, including the one caused by the
removal of kernel/rcu/srcu.c.  Also correct a stray pointer in
 memory-barriers.txt.
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Merge tag '4.13-fixes' of git://git.lwn.net/linux

Pull documentation fixes from Jonathan Corbet:
 "A set of fixes for various warnings, including the one caused by the
  removal of kernel/rcu/srcu.c. Also correct a stray pointer in
  memory-barriers.txt"

* tag '4.13-fixes' of git://git.lwn.net/linux:
  kokr/memory-barriers.txt: Fix obsolete link to atomic_ops.txt
  memory-barriers.txt: Fix broken link to atomic_ops.txt
  docs: Turn off section numbering for the input docs
  docs: Include uaccess docs from the right file
  docs: Do not include from kernel/rcu/srcu.c
2017-07-13 13:44:54 -07:00
SeongJae Park 3afadfd902 memory-barriers.txt: Fix broken link to atomic_ops.txt
Few obsolete links to atomic_ops.txt exist in memory-barriers.txt though
the file has moved to core-api/atomic_ops.rst.  This commit fixes the
obsolete links.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-07-12 16:56:30 -06:00
Linus Torvalds 650fc870a2 There has been a fair amount of activity in the docs tree this time
around.  Highlights include:
 
  - Conversion of a bunch of security documentation into RST
 
  - The conversion of the remaining DocBook templates by The Amazing
    Mauro Machine.  We can now drop the entire DocBook build chain.
 
  - The usual collection of fixes and minor updates.
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Merge tag 'docs-4.13' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "There has been a fair amount of activity in the docs tree this time
  around. Highlights include:

   - Conversion of a bunch of security documentation into RST

   - The conversion of the remaining DocBook templates by The Amazing
     Mauro Machine. We can now drop the entire DocBook build chain.

   - The usual collection of fixes and minor updates"

* tag 'docs-4.13' of git://git.lwn.net/linux: (90 commits)
  scripts/kernel-doc: handle DECLARE_HASHTABLE
  Documentation: atomic_ops.txt is core-api/atomic_ops.rst
  Docs: clean up some DocBook loose ends
  Make the main documentation title less Geocities
  Docs: Use kernel-figure in vidioc-g-selection.rst
  Docs: fix table problems in ras.rst
  Docs: Fix breakage with Sphinx 1.5 and upper
  Docs: Include the Latex "ifthen" package
  doc/kokr/howto: Only send regression fixes after -rc1
  docs-rst: fix broken links to dynamic-debug-howto in kernel-parameters
  doc: Document suitability of IBM Verse for kernel development
  Doc: fix a markup error in coding-style.rst
  docs: driver-api: i2c: remove some outdated information
  Documentation: DMA API: fix a typo in a function name
  Docs: Insert missing space to separate link from text
  doc/ko_KR/memory-barriers: Update control-dependencies example
  Documentation, kbuild: fix typo "minimun" -> "minimum"
  docs: Fix some formatting issues in request-key.rst
  doc: ReSTify keys-trusted-encrypted.txt
  doc: ReSTify keys-request-key.txt
  ...
2017-07-03 21:13:25 -07:00
Palmer Dabbelt f5620df7e3 Documentation: atomic_ops.txt is core-api/atomic_ops.rst
I was reading the memory barries documentation in order to make sure the
RISC-V barries were correct, and I found a broken link to the atomic
operations documentation.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-06-24 08:13:43 -06:00
Stan Drozd 35bdc72a33 docs: Fix typo in Documentation/memory-barriers.txt
This commit changes "architecure" to the correct spelling,
"architecture".

Signed-off-by: Stan Drozd <drozdziak1@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-06-08 08:25:29 -07:00
Linus Torvalds 09d79d1033 Connect the newly RST-formatted documentation to the rest; this had to wait
until the input pull was done.  There's also a few small fixes that
 wandered in.
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Merge tag 'docs-4.12-2' of git://git.lwn.net/linux

Pull more documentation updates from Jonathan Corbet:
 "Connect the newly RST-formatted documentation to the rest; this had to
  wait until the input pull was done. There's also a few small fixes
  that wandered in"

* tag 'docs-4.12-2' of git://git.lwn.net/linux:
  doc: replace FTP URL to kernel.org with HTTPS one
  docs: update references to the device io book
  Documentation: earlycon: fix Marvell Armada 3700 UART name
  docs-rst: add input docs at main index and use kernel-figure
2017-05-11 11:29:52 -07:00
Helmut Grohne 0fe397f0c6 docs: update references to the device io book
While converting the deviceiobook from DocBook to RST, dangling
references were left behind. This commit updates all remaining
references to the new location. SeongJae Park improved the ko_KR
translation.

Fixes: 8a8a602fdb ("docs: Convert the deviceio template to RST")
Signed-off-by: Helmut Grohne <h.grohne@intenta.de>
Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-05-09 13:44:56 -06:00
pierre Kuo b26cfc48e3 doc: Update control-dependencies section of memory-barriers.txt
In the following example, if MAX is defined to be 1, then the compiler
knows (Q % MAX) is equal to zero.  The compiler can therefore throw
away the "then" branch (and the "if"), retaining only the "else" branch.

	q = READ_ONCE(a);
	if (q % MAX) {
		WRITE_ONCE(b, 1);
		do_something();
	} else {
		WRITE_ONCE(b, 2);
		do_something_else();
	}

It is therefore necessary to modify the example like this:

        q = READ_ONCE(a);
-       WRITE_ONCE(b, 1);
+       WRITE_ONCE(b, 2);
        do_something_else();

Signed-off-by: pierre Kuo <vichy.kuo@gmail.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:43 -07:00
Paul E. McKenney c8241f8553 doc: Update control-dependencies section of memory-barriers.txt
This commit adds consistency to examples, formatting, and a couple of
additional warnings.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2017-01-14 21:29:15 -08:00
SeongJae Park 8b9e771555 locking/Documentation: Fix a typo of example result
An example result for data dependent write has a typo.  This commit
fixes the wrong typo.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dhowells@redhat.com
Cc: linux-arch@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1470939463-31950-3-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-08-12 08:24:13 +02:00
SeongJae Park d7cab36db8 locking/Documentation: Fix wrong section reference
Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dhowells@redhat.com
Cc: linux-arch@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1470939463-31950-2-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-08-12 08:24:13 +02:00
SeongJae Park dfeccea617 locking/Documentation: Maintain consistent blank line
Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dhowells@redhat.com
Cc: linux-arch@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1470939463-31950-1-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-08-12 08:24:13 +02:00
Paul E. McKenney ebff09a6ff locking/Documentation: Clarify limited control-dependency scope
Nothing in the control-dependencies section of memory-barriers.txt
says that control dependencies don't extend beyond the end of the
if-statement containing the control dependency.  Worse yet, in many
situations, they do extend beyond that if-statement.  In particular,
the compiler cannot destroy the control dependency given proper use of
READ_ONCE() and WRITE_ONCE().  However, a weakly ordered system having
a conditional-move instruction provides the control-dependency guarantee
only to code within the scope of the if-statement itself.

This commit therefore adds words and an example demonstrating this
limitation of control dependencies.

Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-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>
Cc: corbet@lwn.net
Cc: linux-arch@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/20160615230817.GA18039@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-06-17 09:54:45 +02:00
Will Deacon 3cfe2e8bc1 locking/Documentation: Clarify that ACQUIRE applies to loads, RELEASE applies to stores
For compound atomics performing both a load and a store operation, make
it clear that _acquire and _release variants refer only to the load and
store portions of compound atomic. For example, xchg_acquire is an xchg
operation where the load takes on ACQUIRE semantics.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-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>
Cc: corbet@lwn.net
Cc: dave@stgolabs.net
Cc: dhowells@redhat.com
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/1461691328-5429-3-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-28 10:57:51 +02:00
David Howells 8d4840e848 locking/Documentation: State purpose of memory-barriers.txt
There has been some confusion about the purpose of memory-barriers.txt,
so this commit adds a statement of purpose.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: corbet@lwn.net
Cc: dave@stgolabs.net
Cc: linux-doc@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1461691328-5429-2-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-28 10:57:51 +02:00
Peter Zijlstra e7720af5f9 locking/Documentation: Add disclaimer
It appears people are reading this document as a requirements list for
building hardware. This is not the intent of this document. Nor is it
particularly suited for this purpose.

The primary purpose of this document is our collective attempt to define
a set of primitives that (hopefully) allow us to write correct code on
the myriad of SMP platforms Linux supports.

Its a definite work in progress as our understanding of these platforms,
and memory ordering in general, progresses.

Nor does being mentioned in this document mean we think its a
particularly good idea; the data dependency barrier required by Alpha
being a prime example. Yes we have it, no you're insane to require it
when building new hardware.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: corbet@lwn.net
Cc: dave@stgolabs.net
Cc: dhowells@redhat.com
Cc: linux-doc@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1461691328-5429-1-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-28 10:57:51 +02:00
Davidlohr Bueso 787df6383c locking/Documentation: Mention smp_cond_acquire()
... do this next to smp_load_acquire() when first mentioning
ACQUIRE. While this call is briefly explained and control
dependencies are mentioned later, it does not hurt the reader.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dhowells@redhat.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-7-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13 08:52:23 +02:00
SeongJae Park 0b6fa347dc locking/Documentation: Insert white spaces consistently
The document uses two newlines between sections, one newline between
item and its detailed description, and two spaces between sentences.

There are a few places that used these rules inconsistently - fix them.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-5-git-send-email-paulmck@linux.vnet.ibm.com
[ Fixed the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13 08:52:22 +02:00
SeongJae Park 3dbf0913f6 locking/Documentation: Fix formatting inconsistencies
Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-4-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13 08:52:22 +02:00
SeongJae Park 01e1cd6de8 locking/Documentation: Add missed subsection in TOC
A 'Virtual Machine Guests' subsection was added by this commit:

6a65d26385 ("asm-generic: implement virt_xxx memory barriers")

but the TOC was not updated - update it.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-3-git-send-email-paulmck@linux.vnet.ibm.com
[ Rewrote the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13 08:52:22 +02:00
SeongJae Park 166bda7122 locking/Documentation: Fix missed s/lock/acquire renames
The terms 'lock'/'unlock' were changed to 'acquire'/'release' by the
following commit:

  2e4f5382d1 ("locking/doc: Rename LOCK/UNLOCK to ACQUIRE/RELEASE")

However, the commit missed to change the table of contents - fix that.

Also, the dumb rename changed the section name 'Locking functions' to an
actively misleading 'Acquiring functions' section name.

Rename it to 'Lock acquisition functions' instead.

Suggested-by: David Howells <dhowells@redhat.com>
Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-2-git-send-email-paulmck@linux.vnet.ibm.com
[ Rewrote the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13 08:52:21 +02:00
Paul E. McKenney a5052657c1 locking/Documentation: Clarify relationship of barrier() to control dependencies
The current documentation claims that the compiler ignores barrier(),
which is not the case.  Instead, the compiler carefully pays attention
to barrier(), but in a creative way that still manages to destroy
the control dependency.  This commit sets the story straight.

Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dhowells@redhat.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-1-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13 08:52:21 +02:00
SeongJae Park 65f95ff2e4 documentation: Clarify compiler store-fusion example
The compiler store-fusion example in memory-barriers.txt uses a C
comment to represent arbitrary code that does not update a given
variable.  Unfortunately, someone could reasonably interpret the
comment as instead referring to the following line of code.  This
commit therefore replaces the comment with a string that more
clearly represents the arbitrary code.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14 15:52:19 -07:00
Paul E. McKenney f36fe1e70b documentation: Transitivity is not cumulativity
The "transitivity" section mentions cumulativity in a potentially
confusing way.  Contrary to the current wording, cumulativity is
not transitivity, but rather a hardware discipline that can be used
to implement transitivity on ARM and PowerPC CPUs.  This commit
therefore deletes the mention of cumulativity.

Reported-by: Luc Maranget <luc.maranget@inria.fr>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14 15:52:19 -07:00
Paul E. McKenney 37ef0341ca documentation: Add alternative release-acquire outcome
The memory-barriers.txt discussion of local transitivity and
release-acquire chains leaves out discussion of the outcome of
the read from "u".  This commit therefore adds an outcome showing
that you can get a "1" from this read even if the release-acquire
pairs don't line up.

Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14 15:52:18 -07:00
Paul E. McKenney c535cc9292 documentation: Distinguish between local and global transitivity
The introduction of smp_load_acquire() and smp_store_release() had
the side effect of introducing a weaker notion of transitivity:
The transitivity of full smp_mb() barriers is global, but that
of smp_store_release()/smp_load_acquire() chains is local.  This
commit therefore introduces the notion of local transitivity and
gives an example.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14 15:52:18 -07:00
Paul E. McKenney 92a84dd210 documentation: Subsequent writes ordered by rcu_dereference()
The current memory-barriers.txt does not address the possibility of
a write to a dereferenced pointer.  This should be rare, but when it
happens, we need that write -not- to be clobbered by the initialization.
This commit therefore adds an example showing a data dependency ordering
a later data-dependent write.

Reported-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14 15:52:17 -07:00
Paul E. McKenney 0e4bd2aba3 documentation: Remove obsolete reference to RCU-protected indexes
Commit #1ebee8017d84 (rcu: Eliminate array-index-based RCU primitives)
eliminated the primitives supporting RCU-protected array indexes, but
failed to update Documentation/memory-barriers.txt accordingly.  This
commit therefore removes the discussion of RCU-protected array indexes.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14 15:52:17 -07:00
Paul E. McKenney 895f554222 documentation: Fix memory-barriers.txt section references
This commit fixes a couple of "Compiler Barrier" section references to
be "COMPILER BARRIER".  This makes it easier to find the section in
the usual text editors.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14 15:52:16 -07:00
Paul E. McKenney 7817b799ed documentation: Fix control dependency and identical stores
The summary of the "CONTROL DEPENDENCIES" section incorrectly states that
barrier() may be used to prevent compiler reordering when more than one
leg of the control-dependent "if" statement start with identical stores.
This is incorrect at high optimization levels.  This commit therefore
updates the summary to match the detailed description.

Reported by: Jianyu Zhan <nasa4836@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14 15:52:16 -07:00
Linus Torvalds a200dcb346 virtio: barrier rework+fixes
This adds a new kind of barrier, and reworks virtio and xen
 to use it.
 Plus some fixes here and there.
 
 Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

Pull virtio barrier rework+fixes from Michael Tsirkin:
 "This adds a new kind of barrier, and reworks virtio and xen to use it.

  Plus some fixes here and there"

* tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost: (44 commits)
  checkpatch: add virt barriers
  checkpatch: check for __smp outside barrier.h
  checkpatch.pl: add missing memory barriers
  virtio: make find_vqs() checkpatch.pl-friendly
  virtio_balloon: fix race between migration and ballooning
  virtio_balloon: fix race by fill and leak
  s390: more efficient smp barriers
  s390: use generic memory barriers
  xen/events: use virt_xxx barriers
  xen/io: use virt_xxx barriers
  xenbus: use virt_xxx barriers
  virtio_ring: use virt_store_mb
  sh: move xchg_cmpxchg to a header by itself
  sh: support 1 and 2 byte xchg
  virtio_ring: update weak barriers to use virt_xxx
  Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb"
  asm-generic: implement virt_xxx memory barriers
  x86: define __smp_xxx
  xtensa: define __smp_xxx
  tile: define __smp_xxx
  ...
2016-01-18 16:44:24 -08:00
Michael S. Tsirkin 6a65d26385 asm-generic: implement virt_xxx memory barriers
Guests running within virtual machines might be affected by SMP effects even if
the guest itself is compiled without SMP support.  This is an artifact of
interfacing with an SMP host while running an UP kernel.  Using mandatory
barriers for this use-case would be possible but is often suboptimal.

In particular, virtio uses a bunch of confusing ifdefs to work around
this, while xen just uses the mandatory barriers.

To better handle this case, low-level virt_mb() etc macros are made available.
These are implemented trivially using the low-level __smp_xxx macros,
the purpose of these wrappers is to annotate those specific cases.

These have the same effect as smp_mb() etc when SMP is enabled, but generate
identical code for SMP and non-SMP systems. For example, virtual machine guests
should use virt_mb() rather than smp_mb() when synchronizing against a
(possibly SMP) host.

Suggested-by: David Miller <davem@davemloft.net>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
2016-01-12 20:46:59 +02:00
Linus Torvalds 24af98c4cf Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
 "So we have a laundry list of locking subsystem changes:

   - continuing barrier API and code improvements

   - futex enhancements

   - atomics API improvements

   - pvqspinlock enhancements: in particular lock stealing and adaptive
     spinning

   - qspinlock micro-enhancements"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op
  futex: Cleanup the goto confusion in requeue_pi()
  futex: Remove pointless put_pi_state calls in requeue()
  futex: Document pi_state refcounting in requeue code
  futex: Rename free_pi_state() to put_pi_state()
  futex: Drop refcount if requeue_pi() acquired the rtmutex
  locking/barriers, arch: Remove ambiguous statement in the smp_store_mb() documentation
  lcoking/barriers, arch: Use smp barriers in smp_store_release()
  locking/cmpxchg, arch: Remove tas() definitions
  locking/pvqspinlock: Queue node adaptive spinning
  locking/pvqspinlock: Allow limited lock stealing
  locking/pvqspinlock: Collect slowpath lock statistics
  sched/core, locking: Document Program-Order guarantees
  locking, sched: Introduce smp_cond_acquire() and use it
  locking/pvqspinlock, x86: Optimize the PV unlock code path
  locking/qspinlock: Avoid redundant read of next pointer
  locking/qspinlock: Prefetch the next node cacheline
  locking/qspinlock: Use _acquire/_release() versions of cmpxchg() & xchg()
  atomics: Add test for atomic operations with _relaxed variants
2016-01-11 14:18:38 -08:00
Chris Metcalf f84cfbb0ff Documentation/memory-barriers.txt: Fix ACCESS_ONCE thinko
In commit 2ecf810121 ("Documentation/memory-barriers.txt: Add
needed ACCESS_ONCE() calls to memory-barriers.txt") the statement
"Q = P" was converted to "ACCESS_ONCE(Q) = P".  This should have
been "Q = ACCESS_ONCE(P)".  It later became "WRITE_ONCE(Q, P)".
This doesn't match the following text, which is "Q = LOAD P".
Change the statement to be "Q = READ_ONCE(P)".

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05 12:34:54 -08:00
Davidlohr Bueso 2d142e599b locking/barriers, arch: Remove ambiguous statement in the smp_store_mb() documentation
It serves no purpose but to confuse readers, and is most
likely a left over from constant memory-barriers.txt
updates. I.e.:

  http://lists.openwall.net/linux-kernel/2006/07/15/27

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <linux-arch@vger.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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/1445975631-17047-5-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-12-04 11:39:51 +01:00
Linus Torvalds 105ff3cbf2 atomic: remove all traces of READ_ONCE_CTRL() and atomic*_read_ctrl()
This seems to be a mis-reading of how alpha memory ordering works, and
is not backed up by the alpha architecture manual.  The helper functions
don't do anything special on any other architectures, and the arguments
that support them being safe on other architectures also argue that they
are safe on alpha.

Basically, the "control dependency" is between a previous read and a
subsequent write that is dependent on the value read.  Even if the
subsequent write is actually done speculatively, there is no way that
such a speculative write could be made visible to other cpu's until it
has been committed, which requires validating the speculation.

Note that most weakely ordered architectures (very much including alpha)
do not guarantee any ordering relationship between two loads that depend
on each other on a control dependency:

    read A
    if (val == 1)
        read B

because the conditional may be predicted, and the "read B" may be
speculatively moved up to before reading the value A.  So we require the
user to insert a smp_rmb() between the two accesses to be correct:

    read A;
    if (A == 1)
        smp_rmb()
        read B

Alpha is further special in that it can break that ordering even if the
*address* of B depends on the read of A, because the cacheline that is
read later may be stale unless you have a memory barrier in between the
pointer read and the read of the value behind a pointer:

    read ptr
    read offset(ptr)

whereas all other weakly ordered architectures guarantee that the data
dependency (as opposed to just a control dependency) will order the two
accesses.  As a result, alpha needs a "smp_read_barrier_depends()" in
between those two reads for them to be ordered.

The coontrol dependency that "READ_ONCE_CTRL()" and "atomic_read_ctrl()"
had was a control dependency to a subsequent *write*, however, and
nobody can finalize such a subsequent write without having actually done
the read.  And were you to write such a value to a "stale" cacheline
(the way the unordered reads came to be), that would seem to lose the
write entirely.

So the things that make alpha able to re-order reads even more
aggressively than other weak architectures do not seem to be relevant
for a subsequent write.  Alpha memory ordering may be strange, but
there's no real indication that it is *that* strange.

Also, the alpha architecture reference manual very explicitly talks
about the definition of "Dependence Constraints" in section 5.6.1.7,
where a preceding read dominates a subsequent write.

Such a dependence constraint admittedly does not impose a BEFORE (alpha
architecture term for globally visible ordering), but it does guarantee
that there can be no "causal loop".  I don't see how you could avoid
such a loop if another cpu could see the stored value and then impact
the value of the first read.  Put another way: the read and the write
could not be seen as being out of order wrt other cpus.

So I do not see how these "x_ctrl()" functions can currently be necessary.

I may have to eat my words at some point, but in the absense of clear
proof that alpha actually needs this, or indeed even an explanation of
how alpha could _possibly_ need it, I do not believe these functions are
called for.

And if it turns out that alpha really _does_ need a barrier for this
case, that barrier still should not be "smp_read_barrier_depends()".
We'd have to make up some new speciality barrier just for alpha, along
with the documentation for why it really is necessary.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul E McKenney <paulmck@us.ibm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-11-03 17:22:17 -08:00
Linus Torvalds d63a978865 Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking changes from Ingo Molnar:
 "The main changes in this cycle were:

   - More gradual enhancements to atomic ops: new atomic*_read_ctrl()
     ops, synchronize atomic_{read,set}() ordering requirements between
     architectures, add atomic_long_t bitops.  (Peter Zijlstra)

   - Add _{relaxed|acquire|release}() variants for inc/dec atomics and
     use them in various locking primitives: mutex, rtmutex, mcs, rwsem.
     This enables weakly ordered architectures (such as arm64) to make
     use of more locking related optimizations.  (Davidlohr Bueso)

   - Implement atomic[64]_{inc,dec}_relaxed() on ARM.  (Will Deacon)

   - Futex kernel data cache footprint micro-optimization.  (Rasmus
     Villemoes)

   - pvqspinlock runtime overhead micro-optimization.  (Waiman Long)

   - misc smaller fixlets"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  ARM, locking/atomics: Implement _relaxed variants of atomic[64]_{inc,dec}
  locking/rwsem: Use acquire/release semantics
  locking/mcs: Use acquire/release semantics
  locking/rtmutex: Use acquire/release semantics
  locking/mutex: Use acquire/release semantics
  locking/asm-generic: Add _{relaxed|acquire|release}() variants for inc/dec atomics
  atomic: Implement atomic_read_ctrl()
  atomic, arch: Audit atomic_{read,set}()
  atomic: Add atomic_long_t bitops
  futex: Force hot variables into a single cache line
  locking/pvqspinlock: Kick the PV CPU unconditionally when _Q_SLOW_VAL
  locking/osq: Relax atomic semantics
  locking/qrwlock: Rename ->lock to ->wait_lock
  locking/Documentation/lockstat: Fix typo - lokcing -> locking
  locking/atomics, cmpxchg: Privatize the inclusion of asm/cmpxchg.h
2015-11-03 16:10:43 -08:00
Paul E. McKenney ad2ad5d31f documentation: Add lockless_dereference()
The recently added lockless_dereference() macro is not present in the
Documentation/ directory, so this commit fixes that.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2015-10-06 11:22:57 -07:00
Paul E. McKenney 27566139b6 documentation: No acquire/release for RCU readers
Documentation/memory-barriers.txt calls out RCU as one of the sets
of primitives associated with ACQUIRE and RELEASE.  There really
is an association in that rcu_assign_pointer() includes a RELEASE
operation, but a quick read can convince people that rcu_read_lock() and
rcu_read_unlock() have ACQUIRE and RELEASE semantics, which they do not.

This commit therefore removes RCU from this list in order to avoid
this confusion.

Reported-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2015-10-06 11:22:28 -07:00
Peter Zijlstra e3e72ab80a atomic: Implement atomic_read_ctrl()
Provide atomic_read_ctrl() to mirror READ_ONCE_CTRL(), such that we can
more conveniently use atomics in control dependencies.

Since we can assume atomic_read() implies a READ_ONCE(), we must only
emit an extra smp_read_barrier_depends() in order to upgrade to
READ_ONCE_CTRL() semantics.

Requested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
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: linux-kernel@vger.kernel.org
Cc: oleg@redhat.com
Link: http://lkml.kernel.org/r/20150918115637.GM3604@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-09-23 09:54:29 +02:00