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authorAkinobu Mita <akinobu.mita@gmail.com>2015-09-27 02:09:20 +0900
committerJens Axboe <axboe@fb.com>2015-09-29 11:32:45 -0600
commit4593fdbe7a2f44d5e64c627c715dd0bcec9bdf14 (patch)
treeeb7d2be4cfa44e281f1c17e08b0212d7a405ffe9 /include
parent1356aae08338f1c19ce1c67bf8c543a267688fc3 (diff)
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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 'include')
-rw-r--r--include/linux/blk-mq.h1
-rw-r--r--include/linux/blkdev.h2
2 files changed, 2 insertions, 1 deletions
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 37d1602c4f7a..b80ba4572a31 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -145,7 +145,6 @@ enum {
BLK_MQ_F_SHOULD_MERGE = 1 << 0,
BLK_MQ_F_TAG_SHARED = 1 << 1,
BLK_MQ_F_SG_MERGE = 1 << 2,
- BLK_MQ_F_SYSFS_UP = 1 << 3,
BLK_MQ_F_DEFER_ISSUE = 1 << 4,
BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
BLK_MQ_F_ALLOC_POLICY_BITS = 1,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 99da9ebc7377..19c2e947d4d1 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -456,6 +456,8 @@ struct request_queue {
struct blk_mq_tag_set *tag_set;
struct list_head tag_set_list;
struct bio_set *bio_split;
+
+ bool mq_sysfs_init_done;
};
#define QUEUE_FLAG_QUEUED 1 /* uses generic tag queueing */