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

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Date:	Tue, 26 Jan 2010 17:47:09 -0800
From:	Greg KH <greg@...ah.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Americo Wang <xiyou.wangcong@...il.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>
Subject: Re: [Patch] fix the lockdep warning in tty_fasync()

On Wed, Jan 27, 2010 at 10:09:04AM +0900, KOSAKI Motohiro wrote:
> > 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 :)

Great, I did the same fix, it's now commit id
b04da8bfdfbbd79544cab2fadfdc12e87eb01600 in Linus's tree.

thanks for testing,

greg k-h
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