在 2022/05/20 11:44, Ming Lei 写道:
On Fri, May 20, 2022 at 11:25:42AM +0800, Yu Kuai wrote:Our test report a following crash: BUG: kernel NULL pointer dereference, address: 0000000000000018 PGD 0 P4D 0 Oops: 0000 [#1] SMP NOPTI CPU: 6 PID: 265 Comm: kworker/6:1H Kdump: loaded Tainted: G O 5.10.0-60.17.0.h43.eulerosv2r11.x86_64 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-20220320_160524-szxrtosci10000 04/01/2014 Workqueue: kblockd blk_mq_run_work_fn RIP: 0010:blk_mq_delay_run_hw_queues+0xb6/0xe0 RSP: 0018:ffffacc6803d3d88 EFLAGS: 00010246 RAX: 0000000000000006 RBX: ffff99e2c3d25008 RCX: 00000000ffffffff RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff99e2c911ae18 RBP: ffffacc6803d3dd8 R08: 0000000000000000 R09: ffff99e2c0901f6c R10: 0000000000000018 R11: 0000000000000018 R12: ffff99e2c911ae18 R13: 0000000000000000 R14: 0000000000000003 R15: ffff99e2c911ae18 FS: 0000000000000000(0000) GS:ffff99e6bbf00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000018 CR3: 000000007460a006 CR4: 00000000003706e0 Call Trace: __blk_mq_do_dispatch_sched+0x2a7/0x2c0 ? newidle_balance+0x23e/0x2f0 __blk_mq_sched_dispatch_requests+0x13f/0x190 blk_mq_sched_dispatch_requests+0x30/0x60 __blk_mq_run_hw_queue+0x47/0xd0 process_one_work+0x1b0/0x350 worker_thread+0x49/0x300 ? rescuer_thread+0x3a0/0x3a0 kthread+0xfe/0x140 ? kthread_park+0x90/0x90 ret_from_fork+0x22/0x30 After digging from vmcore, I found that the queue is cleaned up(blk_cleanup_queue() is done) and tag set is freed(blk_mq_free_tag_set() is done). There are two problems here: 1) blk_mq_delay_run_hw_queues() will only be called from __blk_mq_do_dispatch_sched() if e->type->ops.has_work() return true. This seems impossible because blk_cleanup_queue() is done, and there should be no io. Commit ddc25c86b466 ("block, bfq: make bfq_has_work() more accurate") fix the problem in bfq. And currently ohter schedulers don't have such problem. 2) 'hctx->run_work' still exists after blk_cleanup_queue(). blk_mq_cancel_work_sync() is called from blk_cleanup_queue() to cancel all the 'run_work'. However, there is no guarantee that new 'run_work' won't be queued after that(and before blk_mq_exit_queue() is done).It is blk_mq_run_hw_queue() caller's responsibility to grab ->q_usage_counter for avoiding queue cleaned up, so please fix the user side.
Hi, Thanks for your advice. blk_mq_run_hw_queue() can be called async, in order to do that, what I can think of is that grab 'q_usage_counte' before queuing 'run->work' and release it after. Which is very similar to this patch... Kuai
Thanks, Ming .
