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SubjectRe: Linux 3.1-rc9
On Wed, Oct 12, 2011 at 02:35:55PM -0700, Simon Kirby wrote:

> On Sat, Oct 08, 2011 at 09:55:51AM +0200, Peter Zijlstra wrote:
>
> > On Fri, 2011-10-07 at 17:50 -0700, Simon Kirby wrote:
> > > On Fri, Oct 07, 2011 at 08:01:55PM +0200, Peter Zijlstra wrote:
> > >
> > > > @@ -2571,6 +2573,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times);
> > > > static inline void thread_group_cputime_init(struct signal_struct *sig)
> > > > {
> > > > raw_spin_lock_init(&sig->cputimer.lock);
> > > > + raw_spin_lock_init(&sig->cputimer.runtime_lock);
> > >
> > > My 3.1-rc9 tree has just spin_lock_init() here, not raw_*.
> > >
> > > Which tree is your patch against? -next or something?
> >
> > or something yeah.. tip/master I think.
> >
> > > It applies with some cooking like this, but will it be right?
> > >
> > > > sed s/raw_// ../sched-patch-noraw.diff | patch -p1 --dry
> > > patching file include/linux/sched.h
> > > Hunk #1 succeeded at 503 (offset -1 lines).
> > > Hunk #2 succeeded at 512 (offset -1 lines).
> > > Hunk #3 succeeded at 2568 (offset -5 lines).
> > > patching file kernel/posix-cpu-timers.c
> > > patching file kernel/sched_stats.h
> >
> > yes that would be fine.
>
> This patch (s/raw_//) has been stable on 5 boxes for a day. I'll push to
> another 15 shortly and confirm tomorrow. Meanwhile, we had another ~4
> boxes lock up on 3.1-rc9 _with_ d670ec13 reverted (all CPUs spinning),
> but there weren't enough serial cables to log all of them and we haven't
> been lucky enough to capture anything other than what fits on 80x25.
> I'm hoping it's just the same bug you've already fixed. Strangely, boxes
> on -rc6 and -rc7 haven't hit it, but those are across clusters with
> different workloads.

Looks good. No hangs or crashes for two days on any of them running
3.1-rc9 plus this patch. Not sure if you want to deuglify it, but it
seems to work...

Tested-by: Simon Kirby <sim@hostway.ca>

diff against Linus reproduced below.

Simon-

include/linux/sched.h | 3 +++
kernel/posix-cpu-timers.c | 6 +++++-
kernel/sched_stats.h | 4 ++--
3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 41d0237..ad9eafc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -503,6 +503,7 @@ struct task_cputime {
* @running: non-zero when there are timers running and
* @cputime receives updates.
* @lock: lock for fields in this struct.
+ * @runtime_lock: lock for cputime.sum_exec_runtime
*
* This structure contains the version of task_cputime, above, that is
* used for thread group CPU timer calculations.
@@ -511,6 +512,7 @@ struct thread_group_cputimer {
struct task_cputime cputime;
int running;
spinlock_t lock;
+ spinlock_t runtime_lock;
};

#include <linux/rwsem.h>
@@ -2566,6 +2568,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times);
static inline void thread_group_cputime_init(struct signal_struct *sig)
{
spin_lock_init(&sig->cputimer.lock);
+ spin_lock_init(&sig->cputimer.runtime_lock);
}

/*
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index c8008dd..fa189a6 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -284,9 +284,13 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
* it.
*/
thread_group_cputime(tsk, &sum);
+ spin_lock(&cputimer->runtime_lock);
update_gt_cputime(&cputimer->cputime, &sum);
- }
+ } else
+ spin_lock(&cputimer->runtime_lock);
+
*times = cputimer->cputime;
+ spin_unlock(&cputimer->runtime_lock);
spin_unlock_irqrestore(&cputimer->lock, flags);
}

diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index 331e01b..a7e2c1a 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -330,7 +330,7 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
if (!cputimer->running)
return;

- spin_lock(&cputimer->lock);
+ spin_lock(&cputimer->runtime_lock);
cputimer->cputime.sum_exec_runtime += ns;
- spin_unlock(&cputimer->lock);
+ spin_unlock(&cputimer->runtime_lock);
}

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