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SubjectRe: [PATCH v2 1/2] elevator: Fix a race in elevator switching and md device initialization
On Fri, Aug 30, 2013 at 06:47:07PM -0400, Tomoki Sekiyama wrote:
> @@ -739,9 +739,17 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
>
> q->sg_reserved_size = INT_MAX;
>
> + /* Protect q->elevator from elevator_change */
> + mutex_lock(&q->sysfs_lock);
> +
> /* init elevator */
> - if (elevator_init(q, NULL))
> + if (elevator_init(q, NULL)) {
> + mutex_unlock(&q->sysfs_lock);
> return NULL;
> + }
> +
> + mutex_unlock(&q->sysfs_lock);
> +
> return q;
> }
> EXPORT_SYMBOL(blk_init_allocated_queue);
> diff --git a/block/elevator.c b/block/elevator.c
> index 668394d..02d4390 100644
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -186,6 +186,12 @@ int elevator_init(struct request_queue *q, char *name)
> struct elevator_type *e = NULL;
> int err;
>
> + /*
> + * q->sysfs_lock must be held to provide mutual exclusion between
> + * elevator_switch() and here.
> + */
> + lockdep_assert_held(&q->sysfs_lock);
> +
> if (unlikely(q->elevator))
> return 0;

Hmm... why aren't we just changing elevator_init() to grab sysfs_lock
where necessary? It'd be more consistent with elevator_exit() that
way.

Thanks.

--
tejun


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