Commit Graph

22 Commits

Author SHA1 Message Date
Paul E. McKenney ded00a56e9 rcu: remove redundant ACCESS_ONCE definition from rcupreempt.c
Remove the redundant definition of ACCESS_ONCE() from rcupreempt.c in
favor of the one in compiler.h.  Also merge the comment header from
rcupreempt.c's definition into that in compiler.h.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-18 09:45:22 +02:00
Ingo Molnar 82638844d9 Merge branch 'linus' into cpus4096
Conflicts:

	arch/x86/xen/smp.c
	kernel/sched_rt.c
	net/iucv/iucv.c

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-16 00:29:07 +02:00
Ingo Molnar 6c9fcaf2ee Merge branch 'core/rcu' into core/rcu-for-linus 2008-07-15 21:10:12 +02:00
Linus Torvalds 666484f025 Merge branch 'core/softirq' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'core/softirq' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  softirq: remove irqs_disabled warning from local_bh_enable
  softirq: remove initialization of static per-cpu variable
  Remove argument from open_softirq which is always NULL
2008-07-14 15:28:42 -07:00
Ingo Molnar 0c81b2a144 Merge branch 'linus' into core/rcu
Conflicts:

	include/linux/rculist.h
	kernel/rcupreempt.c

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-11 10:46:50 +02:00
Nick Piggin 70ff05554f Fix PREEMPT_RCU without HOTPLUG_CPU
PREEMPT_RCU without HOTPLUG_CPU is broken.  The rcu_online_cpu is called
to initially populate rcu_cpu_online_map with all online CPUs when the
hotplug event handler is installed, and also to populate the map with
CPUs as they come online.  The former case is meant to happen with and
without HOTPLUG_CPU, but without HOTPLUG_CPU, the rcu_offline_cpu
function is no-oped -- while it still gets called, it does not set the
rcu CPU map.

With a blank RCU CPU map, grace periods get to tick by completely
oblivious to active RCU read side critical sections.  This results in
free-before-grace bugs.

Fix is obvious once the problem is known. (Also, change __devinit to
__cpuinit so the function gets thrown away on !HOTPLUG_CPU kernels).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Reported-and-tested-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ Nick is my personal hero of the day - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-10 11:13:44 -07:00
Ingo Molnar 68083e05d7 Merge commit 'v2.6.26-rc9' into cpus4096 2008-07-06 14:23:39 +02:00
Ingo Molnar a60b33cf59 Merge branch 'linus' into core/softirq 2008-06-23 10:52:59 +02:00
Steven Rostedt afd38009cc rcupreempt: remove export of rcu_batches_completed_bh
In rcupreempt, rcu_batches_completed_bh is defined as a static inline in
the header file. This does not need to be exported, and not only that,
this breaks my PPC build.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: paulus@samba.org
Cc: linuxppc-dev@ozlabs.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-06-19 09:45:37 +02:00
Lai Jiangshan 906d882cac rcu: remove unused field struct rcu_data::rcu_tasklet
Since softirq works for rcu reclaimer, rcu_tasklet is unused now.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-06-16 10:11:54 +02:00
Carlos R. Mafra 962cf36c5b Remove argument from open_softirq which is always NULL
As git-grep shows, open_softirq() is always called with the last argument
being NULL

block/blk-core.c:       open_softirq(BLOCK_SOFTIRQ, blk_done_softirq, NULL);
kernel/hrtimer.c:       open_softirq(HRTIMER_SOFTIRQ, run_hrtimer_softirq, NULL);
kernel/rcuclassic.c:    open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
kernel/rcupreempt.c:    open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
kernel/sched.c: open_softirq(SCHED_SOFTIRQ, run_rebalance_domains, NULL);
kernel/softirq.c:       open_softirq(TASKLET_SOFTIRQ, tasklet_action, NULL);
kernel/softirq.c:       open_softirq(HI_SOFTIRQ, tasklet_hi_action, NULL);
kernel/timer.c: open_softirq(TIMER_SOFTIRQ, run_timer_softirq, NULL);
net/core/dev.c: open_softirq(NET_TX_SOFTIRQ, net_tx_action, NULL);
net/core/dev.c: open_softirq(NET_RX_SOFTIRQ, net_rx_action, NULL);

This observation has already been made by Matthew Wilcox in June 2002
(http://www.cs.helsinki.fi/linux/linux-kernel/2002-25/0687.html)

"I notice that none of the current softirq routines use the data element
passed to them."

and the situation hasn't changed since them. So it appears we can safely
remove that extra argument to save 128 (54) bytes of kernel data (text).

Signed-off-by: Carlos R. Mafra <crmafra@ift.unesp.br>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-05-25 07:43:15 +02:00
Mike Travis 363ab6f142 core: use performance variant for_each_cpu_mask_nr
Change references from for_each_cpu_mask to for_each_cpu_mask_nr
where appropriate

Reviewed-by: Paul Jackson <pj@sgi.com>
Reviewed-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-05-23 18:35:12 +02:00
Huang Weiyi 247ab1a805 rcu: remove duplicated include in kernel/rcupreempt.c
Removed duplicated include file <linux/rcupdate.h> in kernel/rcupreempt.c.

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-05-19 10:03:39 +02:00
Paul E. McKenney d7c0651390 rcu: fix rcu_try_flip_waitack_needed() to prevent grace-period stall
The comment was correct -- need to make the code match the comment.
Without this patch, if a CPU goes dynticks idle (and stays there forever)
in just the right phase of preemptible-RCU grace-period processing,
grace periods stall.  The offending sequence of events (courtesy
of Promela/spin, at least after I got the liveness criterion coded
correctly...) is as follows:

o	CPU 0 is in dynticks-idle mode.  Its dynticks_progress_counter
	is (say) 10.

o	CPU 0 takes an interrupt, so rcu_irq_enter() increments CPU 0's
	dynticks_progress_counter to 11.

o	CPU 1 is doing RCU grace-period processing in rcu_try_flip_idle(),
	sees rcu_pending(), so invokes dyntick_save_progress_counter(),
	which in turn takes a snapshot of CPU 0's dynticks_progress_counter
	into CPU 0's rcu_dyntick_snapshot -- now set to 11.  CPU 1 then
	updates the RCU grace-period state to rcu_try_flip_waitack().

o	CPU 0 returns from its interrupt, so rcu_irq_exit() increments
	CPU 0's dynticks_progress_counter to 12.

o	CPU 1 later invokes rcu_try_flip_waitack(), which notices that
	CPU 0 has not yet responded, and hence in turn invokes
	rcu_try_flip_waitack_needed().  This function examines the
	state of CPU 0's dynticks_progress_counter and rcu_dyntick_snapshot
	variables, which it copies to curr (== 12) and snap (== 11),
	respectively.

	Because curr!=snap, the first condition fails.

	Because curr-snap is only 1 and snap is odd, the second
	condition fails.

	rcu_try_flip_waitack_needed() therefore incorrectly concludes
	that it must wait for CPU 0 to explicitly acknowledge the
	counter flip.

o	CPU 0 remains forever in dynticks-idle mode, never taking
	any more hardware interrupts or any NMIs, and never running
	any more tasks.  (Of course, -something- will usually eventually
	happen, which might be why we haven't seen this one in the
	wild.  Still should be fixed!)

Therefore the grace period never ends.  Fix is to make the code match
the comment, as shown below.  With this fix, the above scenario
would be satisfied with curr being even, and allow the grace period
to proceed.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Josh Triplett <josh@kernel.org>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-05-19 10:03:38 +02:00
Paul E. McKenney 4446a36ff8 rcu: add call_rcu_sched()
Fourth cut of patch to provide the call_rcu_sched().  This is again to
synchronize_sched() as call_rcu() is to synchronize_rcu().

Should be fine for experimental and -rt use, but not ready for inclusion.
With some luck, I will be able to tell Andrew to come out of hiding on
the next round.

Passes multi-day rcutorture sessions with concurrent CPU hotplugging.

Fixes since the first version include a bug that could result in
indefinite blocking (spotted by Gautham Shenoy), better resiliency
against CPU-hotplug operations, and other minor fixes.

Fixes since the second version include reworking grace-period detection
to avoid deadlocks that could happen when running concurrently with
CPU hotplug, adding Mathieu's fix to avoid the softlockup messages,
as well as Mathieu's fix to allow use earlier in boot.

Fixes since the third version include a wrong-CPU bug spotted by
Andrew, getting rid of the obsolete synchronize_kernel API that somehow
snuck back in, merging spin_unlock() and local_irq_restore() in a
few places, commenting the code that checks for quiescent states based
on interrupting from user-mode execution or the idle loop, removing
some inline attributes, and some code-style changes.

Known/suspected shortcomings:

o	I still do not entirely trust the sleep/wakeup logic.  Next step
	will be to use a private snapshot of the CPU online mask in
	rcu_sched_grace_period() -- if the CPU wasn't there at the start
	of the grace period, we don't need to hear from it.  And the
	bit about accounting for changes in online CPUs inside of
	rcu_sched_grace_period() is ugly anyway.

o	It might be good for rcu_sched_grace_period() to invoke
	resched_cpu() when a given CPU wasn't responding quickly,
	but resched_cpu() is declared static...

This patch also fixes a long-standing bug in the earlier preemptable-RCU
implementation of synchronize_rcu() that could result in loss of
concurrent external changes to a task's CPU affinity mask.  I still cannot
remember who reported this...

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-05-19 10:01:36 +02:00
Steven Rostedt 8b09dee67f rcupreempt: remove duplicate prototypes
rcu_batches_completed and rcu_patches_completed_bh are both declared
in rcuclassic.h and rcupreempt.h. This patch removes the extra
prototypes for them from rcupdate.h.

rcu_batches_completed_bh is defined as a static inline in the rcupreempt.h
header file. Trying to export this as EXPORT_SYMBOL_GPL causes linking problems
with the powerpc linker. There's no need to export a static inlined function.

Modules must be compiled with the same type of RCU implementation as the
kernel they are for.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-05-19 10:01:35 +02:00
Mike Travis b53e921ba1 generic: reduce stack pressure in sched_affinity
* Modify sched_affinity functions to pass cpumask_t variables by reference
    instead of by value.

  * Use new set_cpus_allowed_ptr function.

Depends on:
	[sched-devel]: sched: add new set_cpus_allowed_ptr function

Cc: Paul Jackson <pj@sgi.com>
Cc: Cliff Wickman <cpw@sgi.com>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-04-19 19:44:59 +02:00
Paul E. McKenney c9e71002aa rcupreempt: remove never-migrates assumption from rcu_process_callbacks()
This patch fixes a potentially invalid access to a per-CPU variable in
rcu_process_callbacks().

This per-CPU access needs to be done in such a way as to guarantee that
the code using it cannot move to some other CPU before all uses of the
value accessed have completed.  Even though this code is currently only
invoked from softirq context, which currrently cannot migrate to some
other CPU, life would be better if this code did not silently make such
an assumption.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-29 20:21:13 +01:00
Paul E. McKenney ae778869ae rcupreempt: fix hibernate/resume in presence of PREEMPT_RCU and hotplug
This fixes a oops encountered when doing hibernate/resume in presence of
PREEMPT_RCU.

The problem was that the code failed to disable preemption when
accessing a per-CPU variable.  This is OK when called from code that
already has preemption disabled, but such is not the case from the
suspend/resume code path.

Reported-by: Dave Young <hidave.darkstar@gmail.com>
Tested-by: Dave Young <hidave.darkstar@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-29 20:21:13 +01:00
Steven Rostedt 2232c2d8e0 rcu: add support for dynamic ticks and preempt rcu
The PREEMPT-RCU can get stuck if a CPU goes idle and NO_HZ is set. The
idle CPU will not progress the RCU through its grace period and a
synchronize_rcu my get stuck. Without this patch I have a box that will
not boot when PREEMPT_RCU and NO_HZ are set. That same box boots fine
with this patch.

This patch comes from the -rt kernel where it has been tested for
several months.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-02-29 18:46:50 +01:00
Paul E. McKenney eaf649e9fe Preempt-RCU: CPU Hotplug handling
This patch allows preemptible RCU to tolerate CPU-hotplug operations.
It accomplishes this by maintaining a local copy of a map of online
CPUs, which it accesses under its own lock.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:25 +01:00
Paul E. McKenney e260be673a Preempt-RCU: implementation
This patch implements a new version of RCU which allows its read-side
critical sections to be preempted. It uses a set of counter pairs
to keep track of the read-side critical sections and flips them
when all tasks exit read-side critical section. The details
of this implementation can be found in this paper -

	http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf

and the article-

	http://lwn.net/Articles/253651/

This patch was developed as a part of the -rt kernel development and
meant to provide better latencies when read-side critical sections of
RCU don't disable preemption.  As a consequence of keeping track of RCU
readers, the readers have a slight overhead (optimizations in the paper).
This implementation co-exists with the "classic" RCU implementations
and can be switched to at compiler.

Also includes RCU tracing summarized in debugfs.

[ akpm@linux-foundation.org: build fixes on non-preempt architectures ]

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Reviewed-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-01-25 21:08:24 +01:00