Messages in this thread | | | From | Tomoki Sekiyama <> | Subject | Re: [PATCH v2 1/2] elevator: Fix a race in elevator switching and md device initialization | Date | Mon, 23 Sep 2013 20:11:55 +0000 |
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Hi Tejun,
Thank you for the review.
On 9/22/13 13:04 , "Tejun Heo" <tj@kernel.org> wrote:
>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?
The locking cannot be moved into elevator_init() because it is called from elevator_switch() path, where the request_queue's sysfs_lock is already taken.
> It'd be more consistent with elevator_exit() that way.
What elevator_exit() locks is elevator_queue's sysfs_lock, not request_queue's sysfs_lock. What we need here is request_queue's sysfs_lock.
>Thanks. > >-- >Tejun
Thanks, Tomoki Sekiyama
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