Date: Fri, 5 Apr 2013 10:18:53 +1100
From: Stephen Rothwell <sfr@canb.auug.org.au>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-next@vger.kernel.org,
        linux-kernel@vger.kernel.org, Nathan Zimmer <nzimmer@sgi.com>
Subject: Re: linux-next: manual merge of the akpm tree with the vfs tree
Message-Id: <20130405101853.769d3b915cacd8a4863b7c19@canb.auug.org.au>
In-Reply-To: <20130404081011.GO21522@ZenIV.linux.org.uk>
References: <20130404172648.27834d12cbb68338f4b89482@canb.auug.org.au>
	<20130403235634.6bc72c39.akpm@linux-foundation.org>
	<20130404000253.2fc9c75d.akpm@linux-foundation.org>
	<20130404081011.GO21522@ZenIV.linux.org.uk>
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Hi Al,

On Thu, 4 Apr 2013 09:10:11 +0100 Al Viro <viro@ZenIV.linux.org.uk> wrote:
>
> On Thu, Apr 04, 2013 at 12:02:53AM -0700, Andrew Morton wrote:
>=20
> > > Well perhaps the vfs tree should start paying some attention to the
> > > rest of the world, particularly after -rc5.
> >=20
> > I can't even find this "lift sb_start_write() out of ->write()".  Not o=
n fsdevel,
> > not on lkml.  What the heck is it and why was it so important?
>=20
> Deadlocks around splice; see the threads re overlayfs/unionmount/aufs and
> deadlocks in their copyup implementations.  See also XFS freeze-related
> deadlocks, etc.
>=20
> The thing is, sb_start_write() is pretty high in locking hierarchy (outsi=
de
> ->i_mutex, etc.), but ->splice_write() and friends had it buried pretty
> deep.  With distinctly unpleasant results, including ->..._write() instan=
ces
> using generic ones (which took the lock) *and* doing some IO outside of t=
hose
> (ext4, for example; ocfs2 also looked fishy in that respect, IIRC).
>=20
> The obvious solution is to lift taking that lock out of the methods, which
> had been done.  It had been discussed on fsdevel and sat in #experimental=
 for
> several weeks; time for it to go into #for-next.

It would have been useful to put something like that in the commit message =
...

--=20
Cheers,
Stephen Rothwell                    sfr@canb.auug.org.au

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