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	Wed, 14 Aug 2024 02:40:57 +0000
Date: Wed, 14 Aug 2024 03:40:57 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: Jeff Layton <jlayton@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mateusz Guzik <mjguzik@gmail.com>,
	Josef Bacik <josef@toxicpanda.com>, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] fs: try an opportunistic lookup for O_CREAT opens too
Message-ID: <20240814024057.GP13701@ZenIV>
References: <20240806-openfast-v2-1-42da45981811@kernel.org>
 <6e5bfb627a91f308a8c10a343fe918d511a2a1c1.camel@kernel.org>
 <20240814021817.GO13701@ZenIV>
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Sender: Al Viro <viro@ftp.linux.org.uk>

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()...