Date:	Thu, 11 Dec 2008 08:32:26 -0800
From:	Greg KH <greg@...ah.com>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, stable@...nel.org,
	linux kernel <linux-kernel@...r.kernel.org>,
	Eric Dumazet <dada1@...mosbay.com>, linux-ext4@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [stable] [PATCH] percpu_counter: Fix __percpu_counter_sum()

On Mon, Dec 08, 2008 at 09:55:23AM -0800, Mingming Cao wrote:
> 在 2008-12-07日的 20:42 -0800，Andrew Morton写道：
> > (cc stable)
> > 
> > On Sun, 7 Dec 2008 10:28:21 -0500 Theodore Tso <tytso@....edu> wrote:
> > 
> > > On Sat, Dec 06, 2008 at 08:22:33PM -0800, Andrew Morton wrote:
> > > > 
> > > > I suggest that what we do is to revert both those changes.  We can
> > > > worry about the possibly-unneeded spin_lock later, in a separate patch.
> > > > 
> > > > It should have been a separate patch anyway.  It's conceptually
> > > > unrelated and is not a bugfix, but it was mixed in with a bugfix.
> > > > 
> > > > Mingming, this needs urgent consideration, please.  Note that I had to
> > > > make additional changes to ext4 due to the subsequent introduction of
> > > > the dirty_blocks counter.
> > > 
> > > I've looked the two patches which you've queued in the -mm branch, and
> > > they look correct to me.
> > > 
> > > The bugs fixed by these patches can potentially lead to filesystem
> > > corruption, since we ultimately use these fields to set the superblock
> > > values.  This in my mind makes them stable candidates at the very
> > > least, and if we weren't so late in the 2.6.28 cycle, I'd be strongly
> > > tempted to push them to Linus as a bugfix before the merge window.
> > > 
> > > Andrew, any strong objections for me to grab them for the ext4 tree?
> > > Or would you rather carry them?  I would prefer that they get pushed
> > > to Linus as soon as the merge window opens, which is one reason why
> > > I'd prefer carry them, but we can do this either way.
> > > 
> > 
> > I'm planning on sending them off to Linus for 2.6.28 this week,
> > assuming nobody can think of a plausible reason to not do that.
> > 
> > Now I didn't look _very_ closely at the chronology, but I think that
> > revert-percpu-counter-clean-up-percpu_counter_sum_and_set.patch reverts
> > a post-2.6.27 change, and is not needed in stable.
> > 
> > revert-percpu_counter-new-function-percpu_counter_sum_and_set.patch
> > however reverts a pre-2.6.27 change, and should be merged into 2.6.27. 
> > This patch reverts the addition and use of
> > percpu_counter_sum_and_set(), which is racy and can corrupt the
> > counters.
> > 
> > However
> > revert-percpu_counter-new-function-percpu_counter_sum_and_set.patch
> > won't apply to 2.6.27 because the dirty_blocks stuff was added and
> > generates rejects.
> > 
> > So if all the above is correct, I'd propose that if and when
> > revert-percpu_counter-new-function-percpu_counter_sum_and_set.patch
> > hits mainline, we should ask the -stable guys to directly revert 
> > 
> 
> Agreed.
> 
> I checked 2.6.27.8, above are correct, the
> revert-percpu-counter-clean-up-percpu_counter_sum_and_set.patch is not
> needed for 2.6.27.x stable tree.

Thanks for letting me know, I'll not include it in the 2.6.27-stable
tree then.

greg k-h
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