diff options
| author | Akinobu Mita <akinobu.mita@gmail.com> | 2015-09-27 02:09:20 +0900 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2015-09-29 11:32:45 -0600 |
| commit | 4593fdbe7a2f44d5e64c627c715dd0bcec9bdf14 (patch) | |
| tree | eb7d2be4cfa44e281f1c17e08b0212d7a405ffe9 /block/blk-mq.c | |
| parent | 1356aae08338f1c19ce1c67bf8c543a267688fc3 (diff) | |
blk-mq: fix sysfs registration/unregistration race
There is a race between cpu hotplug handling and adding/deleting
gendisk for blk-mq, where both are trying to register and unregister
the same sysfs entries.
null_add_dev
--> blk_mq_init_queue
--> blk_mq_init_allocated_queue
--> add to 'all_q_list' (*)
--> add_disk
--> blk_register_queue
--> blk_mq_register_disk (++)
null_del_dev
--> del_gendisk
--> blk_unregister_queue
--> blk_mq_unregister_disk (--)
--> blk_cleanup_queue
--> blk_mq_free_queue
--> del from 'all_q_list' (*)
blk_mq_queue_reinit
--> blk_mq_sysfs_unregister (-)
--> blk_mq_sysfs_register (+)
While the request queue is added to 'all_q_list' (*),
blk_mq_queue_reinit() can be called for the queue anytime by CPU
hotplug callback. But blk_mq_sysfs_unregister (-) and
blk_mq_sysfs_register (+) in blk_mq_queue_reinit must not be called
before blk_mq_register_disk (++) and after blk_mq_unregister_disk (--)
is finished. Because '/sys/block/*/mq/' is not exists.
There has already been BLK_MQ_F_SYSFS_UP flag in hctx->flags which can
be used to track these sysfs stuff, but it is only fixing this issue
partially.
In order to fix it completely, we just need per-queue flag instead of
per-hctx flag with appropriate locking. So this introduces
q->mq_sysfs_init_done which is properly protected with all_q_mutex.
Also, we need to ensure that blk_mq_map_swqueue() is called with
all_q_mutex is held. Since hctx->nr_ctx is reset temporarily and
updated in blk_mq_map_swqueue(), so we should avoid
blk_mq_register_hctx() seeing the temporary hctx->nr_ctx value
in CPU hotplug handling or adding/deleting gendisk .
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-mq.c')
| -rw-r--r-- | block/blk-mq.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c index 2fd7283ec62b..0262131ac5f2 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2035,13 +2035,13 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, goto err_hctxs; mutex_lock(&all_q_mutex); - list_add_tail(&q->all_q_node, &all_q_list); - mutex_unlock(&all_q_mutex); + list_add_tail(&q->all_q_node, &all_q_list); blk_mq_add_queue_tag_set(set, q); - blk_mq_map_swqueue(q); + mutex_unlock(&all_q_mutex); + return q; err_hctxs: |