Messages in this thread | | | Subject | Re: [PATCH 1/1] sched: CPU remove deadlock fix | From | Peter Zijlstra <> | Date | Tue, 09 Dec 2008 15:59:54 +0100 |
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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?
> > Signed-off-by: Brian King <brking@linux.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; > > _
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