linux-kernel - Re: [PATCH] move exit_task_work() before exit

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Message-ID: <54A0A9D5.2010804@hurleysoftware.com>
Date:	Sun, 28 Dec 2014 20:09:41 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Ma, Xindong" <xindong.ma@...el.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Al Viro <viro@...IV.linux.org.uk>
CC:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mhocko@...e.cz" <mhocko@...e.cz>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"ionut.m.alexa@...il.com" <ionut.m.alexa@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Zhang, Di" <di.zhang@...el.com>,
	"Sun, Zhonghua" <zhonghua.sun@...el.com>
Subject: Re: [PATCH] move exit_task_work() before exit_fs().

On 12/28/2014 07:58 PM, Ma, Xindong wrote:
>>
>> On 12/26, Leon Ma wrote:
>>>
>>> We encountered following panic. The scenario is the process is exiting
>>> and executing its task work. When closing dev node, the driver
>>> triggers a firmware reload according to device status. Because task->fs is
>> set to NULL in exit_fs(), panic happens.
>>
>> I think this should be fixed somewhere else...
> Yes, for this panic, I also think driver is not perfect and need a fix. But kernel should not add the limitation like this...
>>
>>> Task work is a common interface, we should not limite the resource the
>> user will utilize.
>>
>> Exactly. And note that with this patch exit_mm()..disassociate_ctty() paths
>> can't use task works.
> I don't get this. Currently disassociate_ctty() is also called after exit_mm() and exit_task_work(). My patch didn't change this.

??

742-	if (group_dead)
743:		disassociate_ctty(1);
744-	exit_task_namespaces(tsk);
745-	exit_task_work(tsk);
746-	exit_thread();

>> Not to mention that this patch moves exit_files() up, even before exit_mm(),
>> without any explanation.
> Moving exit_files() up is because exit_files() closes files and add tasks to task works.
>>
>> Add Al. May be we can move exit_fs() down after exit_task_work(), I dunno,
>> but to me it would be better to change the driver.
>>
> I'm OK with this suggestion to fix this issue. I'm not sure whether in the future task work users will access other resources and expose other issues.
> 

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