Commit e01ad46d authored by Jianchao Wang's avatar Jianchao Wang Committed by Jens Axboe
Browse files

blk-mq: fallback to previous nr_hw_queues when updating fails 



When we try to increate the nr_hw_queues, we may fail due to
shortage of memory or other reason, then blk_mq_realloc_hw_ctxs stops
and some entries in q->queue_hw_ctx are left with NULL. However,
because queue map has been updated with new nr_hw_queues, some cpus
have been mapped to hw queue which just encounters allocation failure,
thus blk_mq_map_queue could return NULL. This will cause panic in
following blk_mq_map_swqueue.

To fix it, when increase nr_hw_queues fails, fallback to previous
nr_hw_queues and post warning. At the same time, driver's .map_queues
usually use completion irq affinity to map hw and cpu, fallback
nr_hw_queues will cause lack of some cpu's map to hw, so use default
blk_mq_map_queues to do that.

Reported-by: default avatar <syzbot+83e8cbe702263932d9d4@syzkaller.appspotmail.com>
Signed-off-by: default avatarJianchao Wang <jianchao.w.wang@oracle.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 34d11ffa

block/blk-mq.c

+24 −3
Original line number Diff line number Diff line
@@ -2557,7 +2557,7 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx( 
static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,

						struct request_queue *q)

{

	int i, j;

	int i, j, end;

	struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;



	/* protect against switching io scheduler  */
@@ -2591,8 +2591,20 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, 
				break;

		}

	}

	/*

	 * Increasing nr_hw_queues fails. Free the newly allocated

	 * hctxs and keep the previous q->nr_hw_queues.

	 */

	if (i != set->nr_hw_queues) {

		j = q->nr_hw_queues;

		end = i;

	} else {

		j = i;

		end = q->nr_hw_queues;

		q->nr_hw_queues = set->nr_hw_queues;

	}



	for (j = i; j < q->nr_hw_queues; j++) {

	for (; j < end; j++) {

		struct blk_mq_hw_ctx *hctx = hctxs[j];



		if (hctx) {
@@ -2604,7 +2616,6 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, 


		}

	}

	q->nr_hw_queues = i;

	mutex_unlock(&q->sysfs_lock);

}
@@ -2989,6 +3000,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 
{

	struct request_queue *q;

	LIST_HEAD(head);

	int prev_nr_hw_queues;



	lockdep_assert_held(&set->tag_list_lock);
@@ -3017,10 +3029,19 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 
		blk_mq_sysfs_unregister(q);

	}



	prev_nr_hw_queues = set->nr_hw_queues;

	set->nr_hw_queues = nr_hw_queues;

	blk_mq_update_queue_map(set);

fallback:

	list_for_each_entry(q, &set->tag_list, tag_set_list) {

		blk_mq_realloc_hw_ctxs(set, q);

		if (q->nr_hw_queues != set->nr_hw_queues) {

			pr_warn("Increasing nr_hw_queues to %d fails, fallback to %d\n",

					nr_hw_queues, prev_nr_hw_queues);

			set->nr_hw_queues = prev_nr_hw_queues;

			blk_mq_map_queues(set);

			goto fallback;

		}

		blk_mq_map_swqueue(q);

	}

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