linux-kernel - Re: [PATCH] task_work: add a scheduling point in task_work

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Message-ID: <50346DB9.7040303@linux.vnet.ibm.com>
Date:	Wed, 22 Aug 2012 13:27:21 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Al Viro <viro@...IV.linux.org.uk>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	". James Morris" <jmorris@...ei.org>,
	linux-security-module@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH] task_work: add a scheduling point in task_work_run()

Hi, Eric

On 08/21/2012 09:05 PM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> It seems commit 4a9d4b02 (switch fput to task_work_add) reintroduced
> the problem addressed in commit 944be0b2 (close_files(): add scheduling
> point)
> 
> If a server process with a lot of files (say 2 million tcp sockets)
> is killed, we can spend a lot of time in task_work_run() and trigger
> a soft lockup.

The thread will be rescheduled if we support kernel preempt, so this
change may only help the case we haven't enabled CONFIG_PREEMPT, isn't
it? What about using ifndef?

And can we make sure that it is safe to sleep(schedule) at this point?
It may need some totally testing to cover all the situation...

Regards,
Michael Wang

> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  kernel/task_work.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 91d4e17..d320d44 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -75,6 +75,7 @@ void task_work_run(void)
>  			p = q->next;
>  			q->func(q);
>  			q = p;
> +			cond_resched();
>  		}
>  	}
>  }
> 
> 
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