Re: [PATCH 1/1] sched: CPU remove deadlock fix

Peter Zijlstra
2008-12-09T14:52:47Z

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?

> 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;
> _