linux-kernel - Re: [writeback] 8bc4ad9498: INFO: suspicious RCU usage. ]

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Date:   Wed, 7 Sep 2016 13:25:54 -0600
From:   Jens Axboe <axboe@...com>
To:     Tejun Heo <tj@...nel.org>,
        kernel test robot <xiaolong.ye@...el.com>
CC:     <lkp@...org>, Jens Axboe <axboe@...nel.dk>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [writeback] 8bc4ad9498: INFO: suspicious RCU usage. ]

On 09/07/2016 10:41 AM, Tejun Heo wrote:
> On Thu, Sep 01, 2016 at 06:21:30PM +0800, kernel test robot wrote:
>>
>> FYI, we noticed the following commit:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git wb-buf-throttle
>> commit 8bc4ad9498f81d6689da42457615db0989e720d3 ("writeback: throttle buffered writeback")
>>
>> in testcase: boot
>>
>> on test machine: qemu-system-x86_64 -enable-kvm -cpu Westmere -m 512M
>>
>> caused below changes:
>>
>>
>> +--------------------------------------+------------+------------+
>> |                                      | b2e4e4e34d | 8bc4ad9498 |
>> +--------------------------------------+------------+------------+
>> | boot_successes                       | 6          | 0          |
>> | boot_failures                        | 0          | 8          |
>> | INFO:suspicious_RCU_usage            | 0          | 8          |
>> | message:INFO:suspicious_RCU_usage    | 0          | 0.0        |
>> | pattern:INFO:suspicious_RCU_usage    | 0          | 0          |
>> | calltrace:disk_events_workfn         | 0          | 8          |
>> | message:calltrace:disk_events_workfn | 0          | 0.0        |
>> | pattern:calltrace:disk_events_workfn | 0          | 0          |
>> +--------------------------------------+------------+------------+
>>
>>
>>
>> [    7.389264] stack backtrace:
>> [    7.391300] CPU: 0 PID: 19 Comm: kworker/0:1 Not tainted 4.8.0-rc4-00008-g8bc4ad9 #1
>> [    7.395279] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
>> [    7.398012] Workqueue: events_freezable_power_ disk_events_workfn
>> [    7.399933]  0000000000000000 ffff88003db1f8e8 ffffffff8178ed3b ffff88003db184c0
>> [    7.404348]  0000000000000001 ffff88003db1f918 ffffffff81123472 ffff88003db184c0
>> [    7.407158]  ffffffff84091180 0000000000000003 ffff880039d4c400 ffff88003db1f938
>> [    7.410074] Call Trace:
>> [    7.411328]  [<ffffffff8178ed3b>] dump_stack+0x82/0xb8
>> [    7.413982]  [<ffffffff81123472>] lockdep_rcu_suspicious+0xf7/0x100
>> [    7.415828]  [<ffffffff817873f4>] bio_blkcg+0x89/0x93
>> [    7.417336]  [<ffffffff817891f0>] check_blkcg_changed+0x58/0x1b8
>
> Hmm... can't reproduce here on qemu with v4.8-rc5 and the same kernel
> config.  Can you please check whether it reproduces on v4.8-rc5?  If
> so, is there any way I can get the qemu image and command line used?

I've been getting them for a while. I just updated the branch to -rc5
this morning, so if it does reproduce, the same mail would likely show
up again. I'll keep you posted :-)

The command line was in the original email:

$ qemu-system-x86_64 -enable-kvm -cpu Westmere -m 512M

And agree, in general it'd be nice if there was a link to the image as
well, so that folks can reproduce.

-- 
Jens Axboe