linux-kernel - Re: [PATCH] signal, procfs: lock_task_sighand() do not need rcu_read

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Date:	Fri, 3 Oct 2008 20:29:15 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH] signal, procfs: lock_task_sighand() do not need rcu_read_lock()

On 10/03, Lai Jiangshan wrote:
>
> lock_task_sighand() make sure task->sighand is being protected,
> so we do not need rcu_read_lock().
> [ exec() will get task->sighand->siglock before change task->sighand! ]
>
> But code using rcu_read_lock() _just_ to protect lock_task_sighand()
> only appear in procfs. (and some code in procfs use lock_task_sighand()
> without such redundant protection.)

Yes, the patch looks correct.

The initial implementaion of lock_task_sighand() did not take RCU lock,
that is why we still have the callers which call rcu_read_lock().
See 1406f2d321bae5ac5ff729dcb773336d9c05ec74.

Thanks!

Oleg.

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