On Mon, Sep 14, 2020 at 10:14 PM Pradeep P V K <ppvk@xxxxxxxxxxxxxx> wrote:
>
> Observes below crash while accessing (use-after-free) lock member
> of bfq data.
>
> context#1 context#2
> process_one_work()
> kthread() blk_mq_run_work_fn()
> worker_thread() ->__blk_mq_run_hw_queue()
> process_one_work() ->blk_mq_sched_dispatch_requests()
> __blk_release_queue() ->blk_mq_do_dispatch_sched()
> ->__elevator_exit()
> ->blk_mq_exit_sched()
> ->exit_sched()
> ->kfree()
> ->bfq_dispatch_request()
> ->spin_unlock_irq(&bfqd->lock)
>
> This is because of the kblockd delayed work that might got scheduled
> around blk_release_queue() and accessed use-after-free member of
> bfq_data.
>
> 240.212359: <2> Unable to handle kernel paging request at
> virtual address ffffffee2e33ad70
> ...
> 240.212637: <2> Workqueue: kblockd blk_mq_run_work_fn
> 240.212649: <2> pstate: 00c00085 (nzcv daIf +PAN +UAO)
> 240.212666: <2> pc : queued_spin_lock_slowpath+0x10c/0x2e0
> 240.212677: <2> lr : queued_spin_lock_slowpath+0x84/0x2e0
> ...
> Call trace:
> 240.212865: <2> queued_spin_lock_slowpath+0x10c/0x2e0
> 240.212876: <2> do_raw_spin_lock+0xf0/0xf4
> 240.212890: <2> _raw_spin_lock_irq+0x74/0x94
> 240.212906: <2> bfq_dispatch_request+0x4c/0xd60
> 240.212918: <2> blk_mq_do_dispatch_sched+0xe0/0x1f0
> 240.212927: <2> blk_mq_sched_dispatch_requests+0x130/0x194
> 240.212940: <2> __blk_mq_run_hw_queue+0x100/0x158
> 240.212950: <2> blk_mq_run_work_fn+0x1c/0x28
> 240.212963: <2> process_one_work+0x280/0x460
> 240.212973: <2> worker_thread+0x27c/0x4dc
> 240.212986: <2> kthread+0x160/0x170
>
> Fix this by cancelling the delayed work if any before elevator exits.
>
> Signed-off-by: Pradeep P V K <ppvk@xxxxxxxxxxxxxx>
> ---
> block/blk-sysfs.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 81722cd..e4a9aac 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -779,6 +779,8 @@ static void blk_release_queue(struct kobject *kobj)
> {
> struct request_queue *q =
> container_of(kobj, struct request_queue, kobj);
> + struct blk_mq_hw_ctx *hctx;
> + int i;
Please move the above two lines to the branch of 'if (queue_is_mq(q)) '.
>
> might_sleep();
>
> @@ -788,9 +790,11 @@ static void blk_release_queue(struct kobject *kobj)
>
> blk_free_queue_stats(q->stats);
>
> - if (queue_is_mq(q))
> + if (queue_is_mq(q)) {
> cancel_delayed_work_sync(&q->requeue_work);
> -
> + queue_for_each_hw_ctx(q, hctx, i)
> + cancel_delayed_work_sync(&hctx->run_work);
> + }
Now the 'cancel_delayed_work_sync' from blk_mq_hw_sysfs_release() can
be killed meantime.
We have to call cancel_delayed_work_sync when reqeuest queue's
refcount drops to zero, otherwise
new run queue may be started somewhere, so feel free to add the
reviewed-by after the above two
comments are addressed.
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks,
Ming Lei
