On 05/19/2015 03:17 AM, tip-bot for Frederic Weisbecker wrote: > Commit-ID: b30f0e3ffedfa52b1d67a302ae5860c49998e5e2 > Gitweb: http://git.kernel.org/tip/b30f0e3ffedfa52b1d67a302ae5860c49998e5e2 > Author: Frederic Weisbecker <fweis...@gmail.com> > AuthorDate: Tue, 12 May 2015 16:41:49 +0200 > Committer: Ingo Molnar <mi...@kernel.org> > CommitDate: Tue, 19 May 2015 08:39:12 +0200 > > sched/preempt: Optimize preemption operations on __schedule() callers > > __schedule() disables preemption and some of its callers > (the preempt_schedule*() family) also set PREEMPT_ACTIVE. > > So we have two preempt_count() modifications that could be performed > at once. > > Lets remove the preemption disablement from __schedule() and pull > this responsibility to its callers in order to optimize preempt_count() > operations in a single place. > > Suggested-by: Linus Torvalds <torva...@linux-foundation.org> > Signed-off-by: Frederic Weisbecker <fweis...@gmail.com> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Thomas Gleixner <t...@linutronix.de> > Link: > http://lkml.kernel.org/r/1431441711-29753-5-git-send-email-fweis...@gmail.com > Signed-off-by: Ingo Molnar <mi...@kernel.org>
Hi all, I was seeing RCU stall warnings that appeared to have different backtrace each time, but would reliably trigger when fuzzing and looked something like this: [4394886.414687] INFO: rcu_preempt detected stalls on CPUs/tasks: [4394886.416717] Tasks blocked on level-0 rcu_node (CPUs 0-23): P13356 [4394886.418699] (detected by 2, t=20502 jiffies, g=3548, c=3547, q=120) [4394886.420712] trinity-c42 R running task 26936 13356 9574 0x10000000 [4394886.422466] ffff8807d1c7fbe8 ffff8807d1c7fb88 0000000000000022 ffff8801081e1bb0 [4394886.423711] ffff8801081e1b88 ffff8807d1eb8780 ffff8801081e11d8 ffff8807e2564000 [4394886.424956] ffff8807d1eb8000 ffff8807d1c7fbd8 ffff8807d1c78000 0000000000000000 [4394886.426196] Call Trace: [4394886.426627] preempt_schedule_irq (./arch/x86/include/asm/paravirt.h:807 kernel/sched/core.c:3218) [4394886.427582] ? lockdep_reset_lock (kernel/locking/lockdep.c:3105) [4394886.428548] ? kill_pid_info (include/linux/rcupdate.h:857 kernel/signal.c:1340) [4394886.429438] retint_kernel (arch/x86/entry/entry_64.S:578) [4394886.430286] ? kill_pid_info (include/linux/rcupdate.h:857 kernel/signal.c:1340) [4394886.431176] ? native_restore_fl (./arch/x86/include/asm/irqflags.h:35) [4394886.432376] lock_is_held (kernel/locking/lockdep.c:3661) [4394886.433241] ? kill_pid_info (include/linux/rcupdate.h:914 kernel/signal.c:1344) [4394886.434135] rcu_read_lock_held (kernel/rcu/update.c:275) [4394886.435012] pid_task (kernel/pid.c:440 (discriminator 5)) [4394886.435656] kill_pid_info (kernel/signal.c:1341) [4394886.436351] ? kill_pid_info (include/linux/rcupdate.h:857 kernel/signal.c:1340) [4394886.437065] SYSC_kill (kernel/signal.c:1426 kernel/signal.c:2903) [4394886.437726] ? SYSC_kill (include/linux/rcupdate.h:857 kernel/signal.c:1425 kernel/signal.c:2903) [4394886.438419] ? find_get_pid (include/linux/rcupdate.h:914 kernel/pid.c:494) [4394886.439134] ? kill_pid (kernel/signal.c:2894) [4394886.439782] ? find_get_pid (kernel/pid.c:497) [4394886.440492] ? find_get_pid (kernel/pid.c:489) [4394886.441183] ? lock_is_held (kernel/locking/lockdep.c:3661) [4394886.441929] ? rcu_read_lock_sched_held (kernel/rcu/update.c:109) [4394886.442772] ? syscall_trace_enter_phase2 (arch/x86/entry/common.c:196) [4394886.443632] SyS_kill (kernel/signal.c:2893) [4394886.444255] tracesys_phase2 (arch/x86/entry/entry_64.S:270) I worked with Paul to rule out RCU as the cause. I've noticed that all traces had one thing in common: being stuck in preempt_schedule_irq(), so I've looked at recent changes there and noticed this commit. I've tried testing the commit before that, and the problem went away. Checking out this commit the problem reappeared. Thanks, Sasha -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
