linux-kernel - Re: NULL pointer dereference at blk_drain

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Date:	Thu, 14 Jun 2012 11:42:15 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Jens Axboe <axboe@...nel.dk>
CC:	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jirislaby@...il.com>, Asias He <asias@...hat.com>
Subject: Re: NULL pointer dereference at blk_drain_queue

On 06/14/2012 11:16 AM, Jens Axboe wrote:
> On 06/14/2012 11:04 AM, Jiri Slaby wrote:
>> Hi,
>>
>> with today's -next I'm (reproducibly) getting this while updating packages:
>> BUG: unable to handle kernel NULL pointer dereference at           (null)
>> IP: [<ffffffff8108cd16>] __wake_up_common+0x26/0x90
>> PGD 463f1067 PUD 463f2067 PMD 0
>> Oops: 0000 [#1] SMP
>> CPU 1
>> Modules linked in:
>> Pid: 2711, comm: kworker/1:0 Not tainted 3.5.0-rc2-next-20120614_64+
>> #1752 Bochs Bochs
>> RIP: 0010:[<ffffffff8108cd16>]  [<ffffffff8108cd16>]
>> __wake_up_common+0x26/0x90
>> RSP: 0018:ffff880047221cb0  EFLAGS: 00010082
>> RAX: 0000000000000086 RBX: ffff880046350888 RCX: 0000000000000000
>> RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff880046350888
>> RBP: ffff880047221cf0 R08: 0000000000000000 R09: 00000001000c0009
>> R10: ffff880047804480 R11: 0000000000000000 R12: ffff880046350890
>> R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000003
>> FS:  0000000000000000(0000) GS:ffff880049700000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> CR2: 0000000000000000 CR3: 0000000045ced000 CR4: 00000000000006e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>> Process kworker/1:0 (pid: 2711, threadinfo ffff880047220000, task
>> ffff8800435bc5c0)
>> Stack:
>>  000000004628da68 0000000000000000 ffff88004970d340 ffff880046350888
>>  0000000000000086 0000000000000003 0000000000000000 0000000000000000
>>  ffff880047221d30 ffffffff8108d9a3 ffff88004970d340 ffff880046350848
>> Call Trace:
>>  [<ffffffff8108d9a3>] __wake_up+0x43/0x70
>>  [<ffffffff81267f96>] blk_drain_queue+0xf6/0x120
>>  [<ffffffff8126803f>] blk_cleanup_queue+0x7f/0xd0
>>  [<ffffffff814a9a80>] md_free+0x50/0x70
>>  [<ffffffff8127b3c2>] kobject_cleanup+0x82/0x1b0
>>  [<ffffffff8127b24b>] kobject_put+0x2b/0x60
>>  [<ffffffff814a97ef>] mddev_delayed_delete+0x2f/0x40
>>  [<ffffffff8107e1ab>] process_one_work+0x11b/0x3f0
>>  [<ffffffff814a97c0>] ? restart_array+0xc0/0xc0
>>  [<ffffffff8107f94e>] worker_thread+0x12e/0x340
>>  [<ffffffff8107f820>] ? manage_workers.isra.29+0x1f0/0x1f0
>>  [<ffffffff81084e1e>] kthread+0x8e/0xa0
>>  [<ffffffff8160add4>] kernel_thread_helper+0x4/0x10
>>  [<ffffffff81084d90>] ? flush_kthread_worker+0x70/0x70
>>  [<ffffffff8160add0>] ? gs_change+0xb/0xb
>> Code: 80 00 00 00 00 55 48 89 e5 41 57 41 89 f7 41 56 41 89 ce 41 55 41
>> 54 4c 8d 67 08 53 48 83 ec 18 89 55 c4 48 8b 57 08 4c 89 45 c8 <4c> 8b
>> 2a 48 8d 42 e8 49 83 ed 18 49 39 d4 75 0d eb 40 0f 1f 84
> 
> It's a bug in local commit bc85cf83, for stacked devices we have not
> initialized the wait queues. So the below should fix it, as would always
> initializing all queue structures even for the partial use case.
> 
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index b477fa0..93eb3e4 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -415,10 +415,12 @@ void blk_drain_queue(struct request_queue *q, bool drain_all)
>  	 * allocation path, so the wakeup chaining is lost and we're
>  	 * left with hung waiters. We need to wake up those waiters.
>  	 */
> -	spin_lock_irq(q->queue_lock);
> -	for (i = 0; i < ARRAY_SIZE(q->rq.wait); i++)
> -		wake_up_all(&q->rq.wait[i]);
> -	spin_unlock_irq(q->queue_lock);
> +	if (q->request_fn) {
> +		spin_lock_irq(q->queue_lock);
> +		for (i = 0; i < ARRAY_SIZE(q->rq.wait); i++)
> +			wake_up_all(&q->rq.wait[i]);
> +		spin_unlock_irq(q->queue_lock);
> +	}

Yes, that fixed it.

thanks,
-- 
js
suse labs
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