Re: [PATCH 1/2 linux-next] Revert "ufs: fix deadlocks introduced by sb mutex merge"

From: Jan Kara <jack@suse.cz>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Fabian Frederick <fabf@skynet.be>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexey Khoroshilov <khoroshilov@ispras.ru>,
	Ian Campbell <ian.campbell@citrix.com>,
	Roger Pau Monne <roger.pau@citrix.com>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>, Jan Kara <jack@suse.cz>,
	xen-devel <xen-devel@lists.xen.org>,
	Evgeniy Dushistov <dushistov@mail.ru>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 1/2 linux-next] Revert "ufs: fix deadlocks introduced by sb mutex merge"
Date: Wed, 17 Jun 2015 10:57:15 +0200	[thread overview]
Message-ID: <20150617085715.GC1614@quack.suse.cz> (raw)
In-Reply-To: <20150605220348.GA14402@ZenIV.linux.org.uk>

On Fri 05-06-15 23:03:48, Al Viro wrote:
> On Fri, Jun 05, 2015 at 07:50:18PM +0100, Al Viro wrote:
> > Basically, we have
> > 	i_mutex: file size changes, contents-affecting syscalls.  Per-inode.
> > 	truncate_mutex: block pointers changes.  Per-inode.
> > 	s_lock:	block and inode bitmaps changes.  Per-filesystem.
> > 
> > For UFS it's slightly more complicated due to tail packing they are doing for
> > short files, but most of that complexity is due to having that stuff handled
> > way too deep in call chain.
> 
> Oh, lovely... commit 10e5dc
> Author: Evgeniy Dushistov <dushistov@mail.ru>
> Date:   Sat Jul 1 04:36:24 2006 -0700
> 
>     [PATCH] ufs: truncate should allocate block for last byte
> 
> had removed ->truncate() method and missed the fact that vmtrucate() had
> callers outside of ->setattr(), such as handling of ->prepare_write() partial
> failures and short copies on write(2) in general.
> 
> Then we had a long and convoluted series of conversions that ended up with
> vmtruncate() lifted into ufs_write_failed() and replaced with
> truncate_pagecache() in there.
> 
> Through all that, everybody (me included) had not noticed that we *still*
> do not free blocks allocated by ufs_write_begin() failing halfway through.
> While we are at it, ufs_write_end() ought to call ufs_write_failed() in
> case when we'd been called after a short copy (and do the same block freeing).
> 
> Joy...  Folks, is anybody actively maintaining fs/ufs these days?

Looking into the changelog there wasn't anyone seriously looking into UFS
for at least 5-6 years... Fabian did some cleanups recently but they were
mostly cosmetic. So I don't think it's really maintained. OTOH clearly
there are some users since occasionally someone comes with a bug report.
Welcome to the world where we have ~50 on disk / network filesystems :-|

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR