Commit da8303c6 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

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



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: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent bc16a4f9

block/blk-core.c

+38 −16
Original line number Diff line number Diff line
@@ -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);

	}

	/* 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

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