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block: make get_request[_wait]() fail if queue is dead

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Currently get_request[_wait]() allocates request whether queue is dead
or not.  This patch makes get_request[_wait]() return NULL if @q is
dead.  blk_queue_bio() is updated to fail the submitted bio if request
allocation fails.  While at it, add docbook comments for
get_request[_wait]().

Note that the current code has rather unclear (there are spurious DEAD
tests scattered around) assumption that the owner of a queue
guarantees that no request travels block layer if the queue is dead
and this patch in itself doesn't change much; however, this will allow
fixing the broken assumption in the next patch.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo 2011-10-19 14:33:05 +02:00 committed by Jens Axboe
parent bc16a4f933
commit da8303c63b
1 changed files with 38 additions and 16 deletions
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54
block/blk-core.c
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@ -709,10 +709,19 @@ static bool blk_rq_should_init_elevator(struct bio *bio)
return true;
}
/*
* Get a free request, queue_lock must be held.
* Returns NULL on failure, with queue_lock held.
* Returns !NULL on success, with queue_lock *not held*.
/**
* get_request - get a free request
* @q: request_queue to allocate request from
* @rw_flags: RW and SYNC flags
* @bio: bio to allocate request for (can be %NULL)
* @gfp_mask: allocation mask
*
* Get a free request from @q. This function may fail under memory
* pressure or if @q is dead.
*
* Must be callled with @q->queue_lock held and,
* Returns %NULL on failure, with @q->queue_lock held.
* Returns !%NULL on success, with @q->queue_lock *not held*.
*/
static struct request *get_request(struct request_queue *q, int rw_flags,
struct bio *bio, gfp_t gfp_mask)
@ -723,6 +732,9 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
const bool is_sync = rw_is_sync(rw_flags) != 0;
int may_queue;
if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
return NULL;
may_queue = elv_may_queue(q, rw_flags);
if (may_queue == ELV_MQUEUE_NO)
goto rq_starved;
@ -815,11 +827,18 @@ out:
return rq;
}
/*
* No available requests for this queue, wait for some requests to become
* available.
/**
* get_request_wait - get a free request with retry
* @q: request_queue to allocate request from
* @rw_flags: RW and SYNC flags
* @bio: bio to allocate request for (can be %NULL)
*
* Called with q->queue_lock held, and returns with it unlocked.
* Get a free request from @q. This function keeps retrying under memory
* pressure and fails iff @q is dead.
*
* Must be callled with @q->queue_lock held and,
* Returns %NULL on failure, with @q->queue_lock held.
* Returns !%NULL on success, with @q->queue_lock *not held*.
*/
static struct request *get_request_wait(struct request_queue *q, int rw_flags,
struct bio *bio)
@ -833,6 +852,9 @@ static struct request *get_request_wait(struct request_queue *q, int rw_flags,
struct io_context *ioc;
struct request_list *rl = &q->rq;
if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
return NULL;
prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
TASK_UNINTERRUPTIBLE);
@ -863,19 +885,15 @@ struct request *blk_get_request(struct request_queue *q, int rw, gfp_t gfp_mask)
{
struct request *rq;
if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
return NULL;
BUG_ON(rw != READ && rw != WRITE);
spin_lock_irq(q->queue_lock);
if (gfp_mask & __GFP_WAIT) {
if (gfp_mask & __GFP_WAIT)
rq = get_request_wait(q, rw, NULL);
} else {
else
rq = get_request(q, rw, NULL, gfp_mask);
if (!rq)
spin_unlock_irq(q->queue_lock);
}
if (!rq)
spin_unlock_irq(q->queue_lock);
/* q->queue_lock is unlocked at this point */
return rq;
@ -1299,6 +1317,10 @@ get_rq:
* Returns with the queue unlocked.
*/
req = get_request_wait(q, rw_flags, bio);
if (unlikely(!req)) {
bio_endio(bio, -ENODEV); /* @q is dead */
goto out_unlock;
}
/*
* After dropping the lock and possibly sleeping here, our request