Re: Hang in work_resched

Guillaume Chazarain
2008-01-30T22:55:02Z

On Jan 29, 2008 11:30 PM, Guillaume Chazarain <guichaz@gmail.com> wrote:
> =======================
> gnome-termina S 00000027 0 2201 1
> f6711fb0 00200082 cb330d62 00000027 f664105c 00000b1e 00000000 cb331880
> 00000027 f660d780 009e3840 080ab7d8 080ab298 f6711000 c0103e7e 009e3840
> 000e0002 00000002 080ab7d8 080ab298 bfb41be8 080ab7d8 0000007b c010007b
> Call Trace:
> [<c0103e7e>] work_resched+0x5/0x16
> =======================
>
> This corresponds to the cli instruction:
> c0103e7e: fa cli

I bisected it, and the resulting commit is appended. Rerverting this
commit applies cleanly on today's git
(dd430ca20c40ecccd6954a7efd13d4398f507728) and makes the hang go away
-:)

commit 37bb6cb4097e29ffee970065b74499cbf10603a3
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri Jan 25 21:08:32 2008 +0100

hrtimer: unlock hrtimer_wakeup

hrtimer_wakeup creates a

base->lock
rq->lock

lock dependancy. Avoid this by switching to HRTIMER_CB_IRQSAFE_NO_SOFTIRQ
which doesn't hold base->lock.

This fully untangles hrtimer locks from the scheduler locks, and allows
hrtimer usage in the scheduler proper.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 061ae28..bd5d6b5 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1293,7 +1293,7 @@ void hrtimer_init_sleeper(struct hrtimer_sleeper
*sl, struct task_struct *task)
sl->timer.function = hrtimer_wakeup;
sl->task = task;
#ifdef CONFIG_HIGH_RES_TIMERS
- sl->timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_RESTART;
+ sl->timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
#endif
}

@@ -1304,6 +1304,8 @@ static int __sched do_nanosleep(struct
hrtimer_sleeper *t, enum hrtimer_mode mod
do {
set_current_state(TASK_INTERRUPTIBLE);
hrtimer_start(&t->timer, t->timer.expires, mode);
+ if (!hrtimer_active(&t->timer))
+ t->task = NULL;

if (likely(t->task))
schedule();

--
Guillaume