This is a note to let you know that I've just added the patch titled

blk-mq: fix race between updating nr_hw_queues and switching io sched

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: blk-mq-fix-race-between-updating-nr_hw_queues-and-switching-io-sched.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Mon Apr 9 13:58:16 CEST 2018

From: Ming Lei ming.lei@redhat.com Date: Sat, 6 Jan 2018 16:27:40 +0800 Subject: blk-mq: fix race between updating nr_hw_queues and switching io sched

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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/blk-mq.c | 4 ++++ 1 file changed, 4 insertions(+)

--- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2314,6 +2314,9 @@ static void blk_mq_realloc_hw_ctxs(struc 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;

@@ -2358,6 +2361,7 @@ static void blk_mq_realloc_hw_ctxs(struc } } q->nr_hw_queues = i; + mutex_unlock(&q->sysfs_lock); blk_mq_sysfs_register(q); }

Patches currently in stable-queue which might be from ming.lei@redhat.com are

queue-4.14/blk-mq-avoid-to-map-cpu-into-stale-hw-queue.patch queue-4.14/blk-mq-fix-kernel-oops-in-blk_mq_tag_idle.patch queue-4.14/blk-mq-fix-race-between-updating-nr_hw_queues-and-switching-io-sched.patch