linux-kernel - Re: linux-next: manual merge of the akpm tree with the vfs tree

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Date:	Fri, 5 Apr 2013 10:18:53 +1100
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Nathan Zimmer <nzimmer@....com>
Subject: Re: linux-next: manual merge of the akpm tree with the vfs tree

Hi Al,

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

-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au

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