linux-kernel - Re: [PATCH v2] fs: try an opportunistic lookup for O

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Message-ID: <df9ee1d9d34b07b9d72a3d8ee8d11c40cf07d193.camel@kernel.org>
Date: Wed, 14 Aug 2024 07:48:17 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Andrew
 Morton <akpm@...ux-foundation.org>, Mateusz Guzik <mjguzik@...il.com>,
 Josef Bacik <josef@...icpanda.com>, linux-fsdevel@...r.kernel.org, 
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fs: try an opportunistic lookup for O_CREAT opens too

On Wed, 2024-08-14 at 03:40 +0100, Al Viro wrote:
> On Wed, Aug 14, 2024 at 03:18:17AM +0100, Al Viro wrote:
> 
> > That's not the only problem; your "is it negative" test is inherently
> > racy in RCU mode.  IOW, what is positive at the time you get here can
> > bloody well go negative immediately afterwards.  Hit that with
> > O_CREAT and you've got a bogus ENOENT...
> 
> Hmm...  OTOH, in that case you end up in step_into(), which will do the
> right thing...
> 
> 	How well does that series survive NFS client regression tests?
> That's where I'd expect potentially subtle shite, what with short-circuited
> ->d_revalidate() on the final pathwalk step in open()...

Christian took in my v3 patch which is a bit different from this one.
It seems to be doing fine in testing with NFS and otherwise.

I don't think we short-circuit the d_revalidate though, do we? That
version calls lookup_fast on the last component which should
d_revalidate the last dentry before returning it.
-- 
Jeff Layton <jlayton@...nel.org>