linux-kernel - Re: [rfcomm_run] WARNING: CPU: 1 PID: 79 at kernel/sched/core.c:7156 __might

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Date:	Thu, 2 Oct 2014 14:54:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	Jet Chen <jet.chen@...el.com>, Su Tao <tao.su@...el.com>,
	Yuanhan Liu <yuanhan.liu@...el.com>, LKP <lkp@...org>,
	linux-kernel@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [rfcomm_run] WARNING: CPU: 1 PID: 79 at kernel/sched/core.c:7156
 __might_sleep()

On Thu, Oct 02, 2014 at 08:38:46AM -0400, Peter Hurley wrote:
> On 10/02/2014 08:31 AM, Peter Zijlstra wrote:
> > On Thu, Oct 02, 2014 at 01:09:27PM +0200, Peter Zijlstra wrote:
> >> On Tue, Sep 30, 2014 at 04:02:28PM +0800, Fengguang Wu wrote:
> >>> Hi Peter,
> >>>
> >>> We possibly find a rfcomm bug (maintainers CCed) exposed by your debug patch
> >>>
> >>> [    1.861895] NET: Registered protocol family 5
> >>> [    1.862978] Bluetooth: RFCOMM TTY layer initialized
> >>> [    1.863099] ------------[ cut here ]------------
> >>> [    1.863105] WARNING: CPU: 1 PID: 79 at kernel/sched/core.c:7156 __might_sleep+0x17d/0x1a1()
> >>> [    1.863112] do not call blocking ops when !TASK_RUNNING; state=1 set at [<c14dc381>] rfcomm_run+0xdf/0x130e
> >>> [    1.863591]  [<c1058b73>] ? kthread_stop+0x53/0x53
> >>> [    1.864906]  [<c155a411>] dump_stack+0x48/0x60
> >>> [    1.866298]  [<c14dc381>] ? rfcomm_run+0xdf/0x130e
> >>
> >> Ha yes, rfcomm_run is a complete buggy mess indeed. Lemme go see what I
> >> can make of it.
> > 
> > ---
> > Subject: rfcomm: Fix broken wait construct
> > 
> > rfcomm_run() is a tad broken in that is has a nested wait loop. One
> > cannot rely on p->state for the outer wait because the inner wait will
> > overwrite it.
> > 
> > While at it, rename rfcomm_schedule to rfcomm_wake, since that is what
> > it actually does.
> 
> rfcomm_schedule() as in schedule_work(), which is how it's used.

Not really, all it does is wake the rfcomm_thread. The thread then does
a linear walk of all known sessions looking for work -- which is clearly
suboptimal as well, but I didn't feel like fixing that.

Also, the current implementation already disagrees with you, all it
basically does it call wake_up_process() which is a big clue right
there.


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