linux-kernel - Re: [PATCH] vfs: fix race in rcu lookup of pruned dentry

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Message-ID: <alpine.LSU.2.00.1107171641130.1274@sister.anvils>
Date:	Sun, 17 Jul 2011 16:47:45 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...nel.dk>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] vfs: fix race in rcu lookup of pruned dentry

On Sun, 17 Jul 2011, Linus Torvalds wrote:
> On Sun, Jul 17, 2011 at 4:16 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > OR
> >
> >  - keep part of the patch from Hugh, treating negative in RCU mode as
> > "need to unlazy".
> 
> No, urgh, that's horrible.
> 
> Not being able to do an RCU lookup of negative dentries would be
> really sad. There are some loads where a negative dentry is the
> *common* case.

Yes, that worried me too.  But I can see Al's point, it looks like
he has enough on his plate for now.

This is not a fresh regression: I vote we make no change for 3.0,
I give your minus-1-liner more testing, hopefully with confirmation,
and we get the fix into 3.0.1 (if that's what stable is to be called).
Or into 3.0 if there's going to be an -rc8, I was assuming not.

Hugh