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Date: Tue, 09 Dec 2008 16:11:56 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Brian King <brking@...ux.vnet.ibm.com> Cc: mingo@...e.hu, efault@....de, vatsa@...ibm.com, balbir@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/1] sched: CPU remove deadlock fix On Tue, 2008-12-09 at 15:59 +0100, Peter Zijlstra wrote: > On Tue, 2008-12-09 at 15:52 +0100, Peter Zijlstra wrote: > > On Tue, 2008-12-09 at 08:47 -0600, Brian King wrote: > > > This patch fixes a possible deadlock scenario in the CPU remove path. > > > migration_call grabs rq->lock, then wakes up everything on rq->migration_queue > > > with the lock held. Then one of the tasks on the migration queue ends up > > > calling tg_shares_up which then also tries to acquire the same rq->lock. > > > > Looks ok, does lockdep agree? > > On second thought, I'm not seeing it at all.. > > why doesn't every wakeup deadlock? because I'm blind... void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr_exclusive, void *key) { unsigned long flags; spin_lock_irqsave(&q->lock, flags); __wake_up_common(q, mode, nr_exclusive, 0, key); spin_unlock_irqrestore(&q->lock, flags); } that's q->lock, not rq->lock... > > > Signed-off-by: Brian King <brking@...ux.vnet.ibm.com> > > > --- > > > > > > kernel/sched.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff -puN kernel/sched.c~sched_cpu_down_deadlock_fix kernel/sched.c > > > --- linux-2.6/kernel/sched.c~sched_cpu_down_deadlock_fix 2008-12-09 08:42:09.000000000 -0600 > > > +++ linux-2.6-bjking1/kernel/sched.c 2008-12-09 08:42:09.000000000 -0600 > > > @@ -6587,7 +6587,9 @@ migration_call(struct notifier_block *nf > > > req = list_entry(rq->migration_queue.next, > > > struct migration_req, list); > > > list_del_init(&req->list); > > > + spin_unlock_irq(&rq->lock); > > > complete(&req->done); > > > + spin_lock_irq(&rq->lock); > > > } > > > spin_unlock_irq(&rq->lock); > > > break; > > > _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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