Messages in this thread Patch in this message | | | From | Sasha Levin <> | Subject | [PATCH AUTOSEL for 4.9 145/281] blk-mq: fix race between updating nr_hw_queues and switching io sched | Date | Mon, 19 Mar 2018 16:00:45 +0000 |
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From: Ming Lei <ming.lei@redhat.com>
[ Upstream commit fb350e0ad99359768e1e80b4784692031ec340e4 ]
In both elevator_switch_mq() and blk_mq_update_nr_hw_queues(), sched tags can be allocated, and q->nr_hw_queue is used, and race is inevitable, for example: blk_mq_init_sched() may trigger use-after-free on hctx, which is freed in blk_mq_realloc_hw_ctxs() when nr_hw_queues is decreased.
This patch fixes the race be holding q->sysfs_lock.
Reviewed-by: Christoph Hellwig <hch@lst.de> Reported-by: Yi Zhang <yi.zhang@redhat.com> Tested-by: Yi Zhang <yi.zhang@redhat.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> --- block/blk-mq.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/block/blk-mq.c b/block/blk-mq.c index a1bef12dd4c4..ac09f61af52c 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1907,6 +1907,9 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx; blk_mq_sysfs_unregister(q); + + /* protect against switching io scheduler */ + mutex_lock(&q->sysfs_lock); for (i = 0; i < set->nr_hw_queues; i++) { int node; @@ -1956,6 +1959,7 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, } } q->nr_hw_queues = i; + mutex_unlock(&q->sysfs_lock); blk_mq_sysfs_register(q); } -- 2.14.1
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