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Subject[PATCH 08/10] block: make get_request[_wait]() fail if queue is dead
Date
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>
Cc: Jens Axboe <axboe@kernel.dk>
---
block/blk-core.c | 54 ++++++++++++++++++++++++++++++++++++++----------------
1 files changed, 38 insertions(+), 16 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 7a90317..fc10f53 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -710,10 +710,19 @@ 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)
@@ -724,6 +733,9 @@ 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;
@@ -816,11 +828,18 @@ 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)
@@ -834,6 +853,9 @@ 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);

@@ -864,19 +886,15 @@ 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;
@@ -1300,6 +1318,10 @@ 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
--
1.7.3.1


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