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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Americo Wang <xiyou.wangcong@gmail.com>
Subject: Re: [Patch] fix the lockdep warning in tty_fasync()
Cc: kosaki.motohiro@jp.fujitsu.com,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Al Viro <viro@zeniv.linux.org.uk>, Tavis Ormandy <taviso@google.com>,
       Jeff Dike <jdike@addtoit.com>, Julien Tinnes <jln@google.com>,
       Matt Mackall <mpm@selenic.com>, LKML <linux-kernel@vger.kernel.org>,
       Oleg Nesterov <oleg@redhat.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Greg KH <greg@kroah.com>
In-Reply-To: <20100126155819.GB3780@hack>
References: <m1ljflxcyl.fsf@fess.ebiederm.org> <20100126155819.GB3780@hack>
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Date: Wed, 27 Jan 2010 10:09:04 +0900 (JST)
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> Commit 703625118 causes a lockdep warning:
>  
> [ INFO: possible irq lock inversion dependency detected ]
> 2.6.33-rc5 #77
> ---------------------------------------------------------
> emacs/1609 just changed the state of lock:
>  (&(&tty->ctrl_lock)->rlock){+.....}, at: [<ffffffff8127c648>]
> tty_fasync+0xe8/0x190
> but this lock took another, HARDIRQ-unsafe lock in the past:
>  (&(&sighand->siglock)->rlock){-.....}
> 
> This is due to we use write_lock_irq() in __f_setown() which turns
> the IRQ on in write_unlock_irq(), causes this warning.
> 
> Switch it to write_lock_irqsave() and write_unlock_irqrestore(),
> as suggested by Eric.
> 
> Reported-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> 
> ---
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index 97e01dc..82cc8a7 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -199,7 +199,8 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
>  static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
>                       int force)
>  {
> -	write_lock_irq(&filp->f_owner.lock);
> +	unsigned long flags;
> +	write_lock_irqsave(&filp->f_owner.lock, flags);
>  	if (force || !filp->f_owner.pid) {
>  		put_pid(filp->f_owner.pid);
>  		filp->f_owner.pid = get_pid(pid);
> @@ -211,7 +212,7 @@ static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
>  			filp->f_owner.euid = cred->euid;
>  		}
>  	}
> -	write_unlock_irq(&filp->f_owner.lock);
> +	write_unlock_irqrestore(&filp->f_owner.lock, flags);
>  }
>  
>  int __f_setown(struct file *filp, struct pid *pid, enum pid_type type,

I've confirmed the warning disappear :)

Thanks.