linux-kernel - Re: VFS deadlock ?

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Message-ID: <20130321202635.GA16406@redhat.com>
Date:	Thu, 21 Mar 2013 16:26:35 -0400
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: VFS deadlock ?

On Thu, Mar 21, 2013 at 01:15:08PM -0700, Linus Torvalds wrote:
 > On Thu, Mar 21, 2013 at 12:29 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
 > >
 > > #0 oddity aside, that looks very much like directory aliased by two different
 > > dentries.  Try to add
 > >         BUG_ON(p1->d_inode == p2->d_inode);
 > > just before
 > >         mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
 > > and see if it triggers.
 > 
 > Don't do a BUG_ON(), instead do something like
 > 
 >    if (WARN_ON_ONCE(p1->d_inode == p2->d_inode)) {
 >         printk("pi=%s p2=%s\n", pi->d_name, p2->d_name);
 >         mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
 >         return NULL;
 >    }

those are qstr's, so I used d_name.name, right ?

 > so that we actually see where it is. I'm assuming it's some sysfs oddity again..

I'd be surprised actually, I've got sysfs excluded from its list of victim files,
due to unrelated issues still unresolved.  So unless it followed a symlink into
sys from somewhere in /proc or /dev...

It took a few hours to reproduce last time, I'll increase the number of child
processes to see if I can trigger it faster now that I have the debug stuff in there.

	Dave
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