From a7e54b6a090ae8a5c203e55cc5aa3f9a91de3bff Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Sat, 6 Jan 2018 16:27:40 +0800 Subject: [PATCH] blk-mq: fix race between updating nr_hw_queues and switching io sched BugLink: http://bugs.launchpad.net/bugs/1763366 [ 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 Reported-by: Yi Zhang Tested-by: Yi Zhang Signed-off-by: Ming Lei Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman Signed-off-by: Thadeu Lima de Souza Cascardo --- block/blk-mq.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 88b9fb184c88..028a19864696 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2403,6 +2403,9 @@ 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; @@ -2447,6 +2450,7 @@ 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); } -- 2.39.5