Re: [PATCH -next v2] blk-mq: fix panic during blk_mq_run_work_fn()

From: Ming Lei <ming.lei@redhat.com>
To: Yu Kuai <yukuai3@huawei.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, yi.zhang@huawei.com
Subject: Re: [PATCH -next v2] blk-mq: fix panic during blk_mq_run_work_fn()
Date: Fri, 20 May 2022 11:44:51 +0800	[thread overview]
Message-ID: <YocOsw6n3y11lNym@T590> (raw)
In-Reply-To: <20220520032542.3331610-1-yukuai3@huawei.com>

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.


Thanks, 
Ming