[Patch] fix the lockdep warning in tty_fasync()

["Américo Wang" <xiyou.wangcong@gmail.com>]

On Tue, Jan 26, 2010 at 04:33:38AM -0800, Eric W. Biederman wrote:
>>>
>>> That or tweak __f_setown to use irqsave/irqrestore variants for it's
>>> locks, __f_setown is already atomic.  I prefer that direction because the
>>> code is just a little simpler.
>>>
>>
>> Oh, very good advice!
>>
>> Patch is below.
>>
>> -------------->
>> 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 ot 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>
>>
>> ----
>>
>> diff --git a/fs/fcntl.c b/fs/fcntl.c
>> index 97e01dc..556b404 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);
>> +	int flags;
>
>Minor nit.  This should be "unsigned long flags;"
>

Right... Below is an updated version.

Thanks.

------------>

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,