* Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> On Mon, 2009-07-20 at 04:12 -0400, Frederic Weisbecker wrote:
>
> > From: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> > Subject: [PATCH] sched: Check if the spinlock is locked in cond_resched_lock()
> >
> > Some uses of cond_resched_lock() might involve an
> > unlocked spinlock, resulting in spurious sleep in
> > atomic warnings.
> > Check whether the spinlock is actually locked and
> > take that into account in the might_sleep() check.
> >
> > Reported-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
> > Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> > ---
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index cb070dc..2789658 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -2294,9 +2294,10 @@ extern int _cond_resched(void);
> >
> > extern int __cond_resched_lock(spinlock_t *lock);
> >
> > -#define cond_resched_lock(lock) ({ \
> > - __might_sleep(__FILE__, __LINE__, PREEMPT_OFFSET); \
> > - __cond_resched_lock(lock); \
> > +#define cond_resched_lock(lock) ({ \
> > + __might_sleep(__FILE__, __LINE__, spin_is_locked(lock) ? \
> > + PREEMPT_OFFSET : 0); \
> > + __cond_resched_lock(lock); \
> > })
> >
> > extern int __cond_resched_softirq(void);
>
>
> No, this looks utterly broken.. who is to say it doesn't get unlocked
> right after that spin_is_locked() check?
>
> cond_resched_lock() callers must hold the lock they use it on, not doing
> so is broken.
>
> So I would suggest something like the below instead:
>
> (utterly untested)
FYI, i've undone the tip:sched/core bits from tip:master for now -
please send a delta patch against tip:sched/core once this is fixed.
Thanks,
Ingo
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