linux-kernel - Re: [Patch] fix the lockdep warning in tty

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Message-Id: <20100127100742.6AD8.A69D9226@jp.fujitsu.com>
Date:	Wed, 27 Jan 2010 10:09:04 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Americo Wang <xiyou.wangcong@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Tavis Ormandy <taviso@...gle.com>,
	Jeff Dike <jdike@...toit.com>, Julien Tinnes <jln@...gle.com>,
	Matt Mackall <mpm@...enic.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, Greg KH <greg@...ah.com>
Subject: Re: [Patch] fix the lockdep warning in tty_fasync()

> 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@...fujitsu.com>
> Signed-off-by: WANG Cong <xiyou.wangcong@...il.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.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.


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