Re: [sched/preempt] INFO: rcu_sched self-detected stall on CPU { 1}

From: Fengguang Wu
Date: Thu Feb 06 2014 - 06:47:03 EST


On Thu, Feb 06, 2014 at 12:27:31PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 06, 2014 at 05:56:46PM +0800, Fengguang Wu wrote:
> > Hi Peter,
> >
> > We noticed the below RCU stalls which will block the system.
> > The problem is bisected to
> >
> > commit 8cb75e0c4ec9786b81439761eac1d18d4a931af3
> > Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > AuthorDate: Wed Nov 20 12:22:37 2013 +0100
> > Commit: Ingo Molnar <mingo@xxxxxxxxxx>
> > CommitDate: Mon Jan 13 17:38:55 2014 +0100
> >
> > sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding
> >
> > arch/x86/include/asm/mwait.h | 2 +-
> > include/linux/preempt.h | 15 +++++++++++++++
> > include/linux/sched.h | 15 +++++++++++++++
> > kernel/cpu/idle.c | 17 ++++++++++-------
> > kernel/sched/core.c | 3 +--
> > 5 files changed, 42 insertions(+), 10 deletions(-)
> >
> > [ 85.786775] INFO: rcu_sched self-detected stall on CPU { 1} (t=15000 jiffies g=233 c=232 q=1940)
>
> Did the initial kernel contain the below?

Nope, so I was testing some old tip sched/core.. Bisect log is

# good: [v3.13-rc1] Linux 3.13-rc1
git bisect good v3.13-rc1
# bad: [130816ce4d5f69167324f7272e70aa3d641677c6] sched, thermal: Clean up preempt_enable_no_resched() abuse
git bisect bad 130816ce4d5f69167324f7272e70aa3d641677c6
# good: [v3.13-rc1] Linux 3.13-rc1
git bisect good v3.13-rc1
# bad: [130816ce4d5f69167324f7272e70aa3d641677c6] sched, thermal: Clean up preempt_enable_no_resched() abuse
git bisect bad 130816ce4d5f69167324f7272e70aa3d641677c6
# skip: [fb00aca474405f4fa8a8519c3179fed722eabd83] rtmutex: Turn the plist into an rb-tree
git bisect skip fb00aca474405f4fa8a8519c3179fed722eabd83
# good: [c9c8986847d2f4fc474c10ee08afa57e7474096d] Merge branch 'x86/idle' into sched/core
git bisect good c9c8986847d2f4fc474c10ee08afa57e7474096d
# bad: [1774e9f3e5c8b38de3b3bc8bd0eacd280f655baf] sched, net: Clean up preempt_enable_no_resched() abuse
git bisect bad 1774e9f3e5c8b38de3b3bc8bd0eacd280f655baf
# bad: [8cb75e0c4ec9786b81439761eac1d18d4a931af3] sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding
git bisect bad 8cb75e0c4ec9786b81439761eac1d18d4a931af3
# first bad commit: [8cb75e0c4ec9786b81439761eac1d18d4a931af3] sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding

Thanks,
Fengguang

> ---
> commit 215393bc1fab3d61a5a296838bdffce22f27ffda
> Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Date: Wed Jan 22 11:24:35 2014 +0100
>
> sched/preempt/x86: Fix voluntary preempt for x86
>
> The #ifdef CONFIG_PREEMPT is both not needed and wrong.
>
> Its not required because asm/preempt.h should provide
> {set,clear}_preempt_need_resched() regardless and its wrong because
> for voluntary preempt we still rely on PREEMPT_NEED_RESCHED.
>
> Reported-and-Tested-by: Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>
> Fixes: 8cb75e0c4ec9 ("sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding")
> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Dipankar Sarma <dipankar@xxxxxxxxxx>
> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
> Link: http://lkml.kernel.org/r/20140122102435.GH31570@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
>
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 59749fc..de83b4e 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -134,7 +134,6 @@ do { \
> #undef preempt_check_resched
> #endif
>
> -#ifdef CONFIG_PREEMPT
> #define preempt_set_need_resched() \
> do { \
> set_preempt_need_resched(); \
> @@ -144,10 +143,6 @@ do { \
> if (tif_need_resched()) \
> set_preempt_need_resched(); \
> } while (0)
> -#else
> -#define preempt_set_need_resched() do { } while (0)
> -#define preempt_fold_need_resched() do { } while (0)
> -#endif
>
> #ifdef CONFIG_PREEMPT_NOTIFIERS
>
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