linux-kernel - Re: processes hung after sys_renameat, and 'missing' processes

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Message-ID: <20120603234042.GR30000@ZenIV.linux.org.uk>
Date:	Mon, 4 Jun 2012 00:40:42 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: processes hung after sys_renameat, and 'missing' processes

On Mon, Jun 04, 2012 at 12:28:20AM +0100, Al Viro wrote:

> Everything in lock_rename() appears to be at lock_rename+0x3e.  Unless
> there's a really huge amount of filesystems on that box, this has to
> be
>                 mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
> and everything on that sucker is not holding any locks yet.  IOW, that's
> the tail hanging off whatever deadlock is there.

Er...  After another look, probably not - it's ->s_vfs_rename_mutex,
so we are seeing one cross-directory rename stuck on something with
all subsequent ones blocked on attempt to grab said mutex.

The interesting one is the guy stuck at lock_rename+0xc9/0xf0, everything
else in lock_rename() is the consequence.
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