linux-kernel - Re: [git pull] vfs and fs fixes

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Message-ID: <20120425152041.GA751@fieldses.org>
Date:	Wed, 25 Apr 2012 11:20:41 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [git pull] vfs and fs fixes

On Wed, Apr 18, 2012 at 05:52:38PM -0400, J. Bruce Fields wrote:
> On Wed, Apr 18, 2012 at 12:44:24AM +0100, Al Viro wrote:
> > On Tue, Apr 17, 2012 at 03:08:26PM -0700, Linus Torvalds wrote:
> > > > Or I could increment that counter for all the conflicting operations and
> > > > rely on it instead of the i_mutex. ?I was trying to avoid adding
> > > > something like that (an inc, a dec, another error path) to every
> > > > operation. ?And hoping to avoid adding another field to struct inode.
> > > > Oh well.
> > > 
> > > We could just say that we can do a double inode lock, but then
> > > standardize on the order. And the only sane order is comparing inode
> > > pointers, not inode numbers like ext4 apparently does.
> > > 
> > > With a standard order, I don't think it would be at all wrong to just
> > > take the inode lock on rename.
> > 
> > In principle, yes, but have you tried to grep for i_mutex?  Note that
> > we have *another* place where multiple ->i_mutex might be held on
> > non-directories (and unless I'm missing something, ext4 move_extent.c
> > stuff doesn't play well with it): quota writes.  Which can, AFAICS,
> > happen while write(2) is holding ->i_mutex on a regular file.  So
> > it's not _that_ easy - we want something like "and quota file is goes
> > last"
> 
> So the idea would be to always take the i_mutex on non-quota files
> before taking it on quota files?
> 
> I tried pulling the ext4 thing into fs/inode.c, modifying the order to
> do that, and then doing the rename change on top of that.

Patches follow, with the ordering change at the end.

And a documentation fix that I suppose could go in whenever.

--b.
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