linux-kernel - Re: [PATCH v1 0/3] Allow knfsd to use atomic

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Message-ID: <5765310C-1F30-465A-82EF-38FFA7A20E7F@hammerspace.com>
Date: Tue, 18 Nov 2025 12:17:24 -0500
From: Benjamin Coddington <bcodding@...merspace.com>
To: Chuck Lever <chuck.lever@...cle.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Jeff Layton <jlayton@...nel.org>, NeilBrown <neil@...wn.name>,
 Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>,
 Tom Talpey <tom@...pey.com>, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
 Trond Myklebust <trondmy@...nel.org>, Mike Snitzer <snitzer@...nel.org>
Subject: Re: [PATCH v1 0/3] Allow knfsd to use atomic_open()

On 18 Nov 2025, at 11:58, Chuck Lever wrote:

> On 11/18/25 11:33 AM, Benjamin Coddington wrote:
>> We have workloads that will benefit from allowing knfsd to use atomic_open()
>> in the open/create path.  There are two benefits; the first is the original
>> matter of correctness: when knfsd must perform both vfs_create() and
>> vfs_open() in series there can be races or error results that cause the
>> caller to receive unexpected results.
>
> Commit fb70bf124b05 ("NFSD: Instantiate a struct file when creating a
> regular NFSv4 file") was supposed to address this. If there are still
> issues, then a Fixes: tag and some explanation of where there are gaps
> would be welcome in the commit message or cover letter. We might need
> to identify LTS backport requirements, in that case.

The problem was noticed on a test that did open O_CREAT with mode 0 which
will succeed in creating the file but will return -EACCES from vfs_open() -
this specific test is mentioned in 3/3 description.  Insane case, but I
suppose someone might want it to behave properly.

Thanks for the commit pointer, I will check out the BugLink on it.  I will
add the Fixes tag in the next version if one emerges.

Ben