linux-kernel - Re: WARNING: CPU: 3 PID: 1568 at kernel/sched/core.c:7738 __might

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Date:   Mon, 12 Dec 2016 14:30:34 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, Shaohua Li <shli@...com>
Subject: Re: WARNING: CPU: 3 PID: 1568 at kernel/sched/core.c:7738 __might_sleep+0x69/0x7e

On Mon, Dec 12, 2016 at 2:03 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello, Michal.
>
> On Fri, Dec 09, 2016 at 04:12:29PM +0100, Michal Hocko wrote:
>> At first I thought this would be related to you recent work
>> http://lkml.kernel.org/r/1477673892-28940-1-git-send-email-tj@kernel.org
>> but that doesn't seem to be in the linux-next I am using as a base.
>> io_schedule_timeout is on the stack though so you might have an idea
>> what is going on here. That might_sleep check has been added a long ago
>> 02e7cf8f8488 ("ide-cd,atapi: use bio for internal commands") in 2.6.31
>> so I am wondering what has changed since than.
>
> 10d784eae2b4 ("sched: always use blk_schedule_flush_plug in
> io_schedule_out") seems related.  might_sleep is complaining that it's
> being called while !TASK_RUNNING.  Shaohua, any ideas?

Yeah, it is pretty much similar to the one I fixed for networking:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d9dc8b0f8b4ec8cdc48ad5a20a3105387138be82

But in your case, it is complicated because of the wait bits API.