On Tue, Sep 15, 2020 at 02:41:02PM +0530, Pradeep P V K 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() Just found __blk_release_queue killed in v5.9 cycle. > ->__elevator_exit() > ->blk_mq_exit_sched() > ->exit_sched() > ->kfree() > ->bfq_dispatch_request() > ->spin_unlock_irq(&bfqd->lock) Actually not sure if the above race is easy to trigger in recent kernel, because we do call cancel_delayed_work_sync() in blk_mq_hw_sysfs_release(), which is usually called before __elevator_exit() from blk_exit_queue()/blk_release_queue(). So can you share your kernel version in which the issue is reproduced? And can you reproduce this issue on v5.8 or v5.9-rc5? > > 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. > > Changes since V1: > - Moved the logic into blk_cleanup_queue() as per Ming comments. > > Signed-off-by: Pradeep P V K <ppvk@xxxxxxxxxxxxxx> > --- > block/blk-mq.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 4abb714..890fded 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2598,6 +2598,7 @@ static void blk_mq_exit_hw_queues(struct request_queue *q, > break; > blk_mq_debugfs_unregister_hctx(hctx); > blk_mq_exit_hctx(q, set, hctx, i); > + cancel_delayed_work_sync(&hctx->run_work); > } > } It should be better to move cancel_delayed_work_sync() into blk_mq_exit_hctx(), exactly before adding hctx into unused list. Thanks, Ming
