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

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Message-ID: <20120603231709.GP30000@ZenIV.linux.org.uk>
Date:	Mon, 4 Jun 2012 00:17:09 +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


> Also, sysrq-w is usually way more interesting than 't' when there are
> processes stuck on a mutex.
> 
> Because yes, it looks like you have a boattload of trinity processes
> stuck on an inode mutex. Looks like every single one of them is in
> 'lock_rename()'. It *shouldn't* be an ABBA deadlock, since lockdep
> should have noticed that, but who knows.

lock_rename() is a bit of a red herring here - they appear to be all
within-directory renames, so it's just a "trying to rename something
in a directory that has ->i_mutex held by something else".

IOW, something else in there is holding ->i_mutex - something that
either hadn't been through lock_rename() at all or has already
passed through it and still hadn't got around to unlock_rename().
In either case, suspects won't have lock_rename() in the trace...
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