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From: "J. Bruce Fields" <bfields@fieldses.org>
To: Jeff Layton <jlayton@kernel.org>
Cc: Greg KH <gregkh@linuxfoundation.org>,
	Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, skhan@linuxfoundation.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	syzbot+e6d5398a02c516ce5e70@syzkaller.appspotmail.com
Subject: Re: [PATCH v2 1/2] fcntl: fix potential deadlocks for &fown_struct.lock
Date: Wed, 7 Jul 2021 09:51:29 -0400	[thread overview]
Message-ID: <20210707135129.GA9446@fieldses.org> (raw)
In-Reply-To: <4dda1cad6348fced5fcfcb6140186795ed07d948.camel@kernel.org>

On Wed, Jul 07, 2021 at 07:40:47AM -0400, Jeff Layton wrote:
> On Wed, 2021-07-07 at 12:51 +0200, Greg KH wrote:
> > On Wed, Jul 07, 2021 at 06:44:42AM -0400, Jeff Layton wrote:
> > > On Wed, 2021-07-07 at 08:05 +0200, Greg KH wrote:
> > > > On Wed, Jul 07, 2021 at 10:35:47AM +0800, Desmond Cheong Zhi Xi wrote:
> > > > > +	WARN_ON_ONCE(irqs_disabled());
> > > > 
> > > > If this triggers, you just rebooted the box :(
> > > > 
> > > > Please never do this, either properly handle the problem and return an
> > > > error, or do not check for this.  It is not any type of "fix" at all,
> > > > and at most, a debugging aid while you work on the root problem.
> > > > 
> > > > thanks,
> > > > 
> > > > greg k-h
> > > 
> > > Wait, what? Why would testing for irqs being disabled and throwing a
> > > WARN_ON in that case crash the box?
> > 
> > If panic-on-warn is enabled, which is a common setting for systems these
> > days.
> 
> Ok, that makes some sense.

Wait, I don't get it.

How are we supposed to decide when to use WARN, when to use BUG, and
when to panic?  Do we really want to treat them all as equivalent?  And
who exactly is turning on panic-on-warn?

--b.

WARNING: multiple messages have this Message-ID (diff)
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Jeff Layton <jlayton@kernel.org>
Cc: syzbot+e6d5398a02c516ce5e70@syzkaller.appspotmail.com,
	linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
	linux-fsdevel@vger.kernel.org,
	Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [PATCH v2 1/2] fcntl: fix potential deadlocks for &fown_struct.lock
Date: Wed, 7 Jul 2021 09:51:29 -0400	[thread overview]
Message-ID: <20210707135129.GA9446@fieldses.org> (raw)
In-Reply-To: <4dda1cad6348fced5fcfcb6140186795ed07d948.camel@kernel.org>

On Wed, Jul 07, 2021 at 07:40:47AM -0400, Jeff Layton wrote:
> On Wed, 2021-07-07 at 12:51 +0200, Greg KH wrote:
> > On Wed, Jul 07, 2021 at 06:44:42AM -0400, Jeff Layton wrote:
> > > On Wed, 2021-07-07 at 08:05 +0200, Greg KH wrote:
> > > > On Wed, Jul 07, 2021 at 10:35:47AM +0800, Desmond Cheong Zhi Xi wrote:
> > > > > +	WARN_ON_ONCE(irqs_disabled());
> > > > 
> > > > If this triggers, you just rebooted the box :(
> > > > 
> > > > Please never do this, either properly handle the problem and return an
> > > > error, or do not check for this.  It is not any type of "fix" at all,
> > > > and at most, a debugging aid while you work on the root problem.
> > > > 
> > > > thanks,
> > > > 
> > > > greg k-h
> > > 
> > > Wait, what? Why would testing for irqs being disabled and throwing a
> > > WARN_ON in that case crash the box?
> > 
> > If panic-on-warn is enabled, which is a common setting for systems these
> > days.
> 
> Ok, that makes some sense.

Wait, I don't get it.

How are we supposed to decide when to use WARN, when to use BUG, and
when to panic?  Do we really want to treat them all as equivalent?  And
who exactly is turning on panic-on-warn?

--b.
_______________________________________________
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Linux-kernel-mentees@lists.linuxfoundation.org
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  reply	other threads:[~2021-07-07 13:51 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-07  2:35 [PATCH v2 0/2] fcntl: fix potential deadlocks Desmond Cheong Zhi Xi
2021-07-07  2:35 ` Desmond Cheong Zhi Xi
2021-07-07  2:35 ` [PATCH v2 1/2] fcntl: fix potential deadlocks for &fown_struct.lock Desmond Cheong Zhi Xi
2021-07-07  2:35   ` Desmond Cheong Zhi Xi
2021-07-07  6:05   ` Greg KH
2021-07-07  6:05     ` Greg KH
2021-07-07  6:54     ` Desmond Cheong Zhi Xi
2021-07-07  6:54       ` Desmond Cheong Zhi Xi
2021-07-07 10:44     ` Jeff Layton
2021-07-07 10:44       ` Jeff Layton
2021-07-07 10:51       ` Greg KH
2021-07-07 10:51         ` Greg KH
2021-07-07 11:40         ` Jeff Layton
2021-07-07 11:40           ` Jeff Layton
2021-07-07 13:51           ` J. Bruce Fields [this message]
2021-07-07 13:51             ` J. Bruce Fields
2021-07-07 15:06             ` Greg KH
2021-07-07 15:06               ` Greg KH
2021-07-07 15:19               ` J. Bruce Fields
2021-07-07 15:19                 ` J. Bruce Fields
2021-07-07 15:31                 ` Greg KH
2021-07-07 15:31                   ` Greg KH
2021-07-07 15:34                   ` J. Bruce Fields
2021-07-07 15:34                     ` J. Bruce Fields
2021-07-07 15:46                     ` Greg KH
2021-07-07 15:46                       ` Greg KH
2021-07-07 16:18                       ` Jeff Layton
2021-07-07 16:18                         ` Jeff Layton
2021-07-07 16:25                         ` Matthew Wilcox
2021-07-07 16:25                           ` Matthew Wilcox
2021-07-07 17:52                           ` Jeff Layton
2021-07-07 17:52                             ` Jeff Layton
2021-07-07 17:58                           ` Eric Biggers
2021-07-07 17:58                             ` Eric Biggers
2021-07-07  2:35 ` [PATCH v2 2/2] fcntl: fix potential deadlock for &fasync_struct.fa_lock Desmond Cheong Zhi Xi
2021-07-07  2:35   ` Desmond Cheong Zhi Xi

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