linux-kernel - Re: Linux 3.19-rc5

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Date:	Wed, 21 Jan 2015 17:54:00 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Davidlohr Bueso <dave@...olabs.net>,
	Bruno Prémont <bonbons@...ux-vserver.org>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	tglx@...utronix.de, ilya.dryomov@...tank.com,
	umgwanakikbuti@...il.com, oleg@...hat.com
Subject: Re: Linux 3.19-rc5

On 01/21/2015 05:12 PM, Davidlohr Bueso wrote:
> On Wed, 2015-01-21 at 22:37 +0100, Bruno Prémont wrote:
>> On Wed, 21 January 2015 Bruno Prémont wrote:
>>> On Tue, 20 January 2015 Linus Torvalds wrote:
>>>> On Tue, Jan 20, 2015 at 6:02 AM, Bruno Prémont wrote:
>>>>>
>>>>> No idea yet which rc is the offender (nor exact patch), but on my not
>>>>> so recent UP laptop with a pccard slot I have 2 pccardd kernel threads
>>>>> converting my laptop into a heater.

[...]

>> Bisecting to the end did point me at (the warning traces produced in great
>> quantities might not be the very same issue as the abusive CPU usage, but
>> certainly look very related):
>>   [CCing people on CC for the patch]
>>
>> commit 8eb23b9f35aae413140d3fda766a98092c21e9b0
>> Author: Peter Zijlstra <peterz@...radead.org>
>> Date:   Wed Sep 24 10:18:55 2014 +0200

[...]

>> Which does produce the following trace (hand-copied most important parts of it):
>>   Warning: CPU 0 PID: 68 at kernel/sched/core.c:7311 __might_sleep+0x143/0x170
>>   do not call blocking ops when !TASK_RUNNING; state=1 set at [<c1436390>] pccardd+0xa0/0x3e0
>>   ...
>>   Call trace:
>>     ...
>>     __might_sleep+0x143/0x170
>>     ? pccardd+0xa0/0x3e0
>>     ? pccardd+0xa0/0x3e0
>>     mutex_lock+0x17/0x2a
>>     pccardd+0xe9/0x3e0
>>     ? pcmcia_socket_uevent+0x30/0x30
>>
>> pccardd() is located in drivers/pcmcia/cs.c and seems to be of the structure
>> Peter's patch wants to warn about.
> 
> Yeah setting current to interruptable so early in the game is bogus. It
> should be set after unlocking the skt_mutex.

Yeah, but the debug check is triggering worse behavior, requiring
bisecting back to the debug commit.

How does the might_sleep() check here guarantee the task won't sleep?

Regards,
Peter Hurley

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