From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F21702D8DB7 for ; Wed, 3 Dec 2025 12:26:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764764779; cv=none; b=NeT37qvZH9l714rC12qACScDZkjQ7wduEW/CgwZZmP5OBXzOpxVhrlxIbsN8hoLb8YV3ag1C2bbFmnTgpPz2tTA1gLSLX4SLmFIWEyg8u72y4XxQ81GemqC97K8uLmQ6isvNVzI602KeS01yNbcnvyxB7qBaHGKKBvB8hiHj0DM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764764779; c=relaxed/simple; bh=RzOO0t8NS9yCiB5WJt+5PGVRlXgLAzZk5byIPBg65Xk=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=CXQocwk1uxaAnRE/JVfsO0DyHWDAHAgWqiHaamPWcIg7wbTH59VKhvl3cB6uldGFXj6uapOUs4YMV1+Piss8ZeZ98+FbKiMSeho7Zvf8TED0O1kfhtsQoh1qyuH3GIdJSD3anYhV4I4fzoPZkIDzDMWaqFABxK5U59o74gMikbw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=H/zqGIK1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="H/zqGIK1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D0C6BC4CEFB; Wed, 3 Dec 2025 12:26:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764764778; bh=RzOO0t8NS9yCiB5WJt+5PGVRlXgLAzZk5byIPBg65Xk=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=H/zqGIK1iczMM/QtATl1nezS2NjSQySxUviylni2fMqY6yatNJa4uZRvdFw83Hq2O my+JjnjuJu53WavTtQR4+rMaNEU+X720QxTbc3KSqlbzwpESOW2h9qel1+b81xvXGR DixwHJUWxSeojBR8Ap9AIA0Ra9B7XLauJ1TEBgsbFkZBAT0mYxIgh4fKDDVBVs7OMl 36vTgVeZp5OYQFWjLr9l2GOJeC9vgYdZfyEntUEm+eE13YT6PvsKApm9tBbu/1ASdW D+hWeJLRJmWR+iCT83tCxMBgGmvauBQzYNaI8GLhklxiqEXk7ZpGGvyow+lai7YsVV IIWWcVZBeJUAQ== Message-ID: Subject: Re: [PATCH v2 1/2] nfsd: prevent write delegations when client has existing opens From: Jeff Layton To: NeilBrown , Chuck Lever Cc: Olga Kornievskaia , Dai Ngo , Tom Talpey , linux-nfs@vger.kernel.org, Chuck Lever Date: Wed, 03 Dec 2025 07:26:16 -0500 In-Reply-To: <176472909957.16766.8691035364646019081@noble.neil.brown.name> References: <20251202224208.4449-1-cel@kernel.org> , <176471811359.16766.18131279195615642514@noble.neil.brown.name> , <176472909957.16766.8691035364646019081@noble.neil.brown.name> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Wed, 2025-12-03 at 13:31 +1100, NeilBrown wrote: > On Wed, 03 Dec 2025, Chuck Lever wrote: > >=20 > > On Tue, Dec 2, 2025, at 6:28 PM, NeilBrown wrote: > > > On Wed, 03 Dec 2025, Chuck Lever wrote: > > > > From: Chuck Lever > > > >=20 > > > > When a client holds an existing OPEN stateid for a file and then > > > > requests a new OPEN that could receive a write delegation, the > > > > server must not grant that delegation. A write delegation promises > > > > the client it can handle "all opens" locally, but this promise is > > > > violated when the server is already tracking open state for that > > > > same client. > > >=20 > > > Can you please spell out how the promise is violated? > > > Where RFC 8881, section 10.4 says > > >=20 > > > An OPEN_DELEGATE_WRITE delegation allows the client to handle, on = its > > > own, all opens.=20 > > >=20 > > > I interpret that to mean that all open *requests* from the applicatio= n can > > > now be handled without reference to the server. > > > I don't think that "all opens" can reasonably refer to "all existing = or > > > future open state for the file". Is that how you interpret it? > >=20 > > It is: as long as a client holds a write delegation stateid, that=E2=80= =99s a > > promise that the server will inform that client when any other client > > wants to open that file. In other words, an NFS server can=E2=80=99t of= fer a > > write delegation to a client if there is another OPEN on that file. >=20 > Agreed: "other" client and "another" OPEN. >=20 > >=20 > > The issue here is about an OPEN that occurred in the past and is still > > active, not a future OPEN. NFSD was checking for OPENs that other > > clients had for a file before offering a write delegation, but it does = not > > currently check if the /requesting client/ itself has an OPEN stateid f= or > > that file. > >=20 >=20 > I don't see a problem with offering a write delegation when the client > previously had the same file open. > Note that a client only ever has one stateid for any given file. If it > opens the same file again, it will get the same stateid - with seqid > incremented. If it closes the stateid, then it will not have that file > open at all any more. >=20 > If the client has the file open for READ, then opens again for WRITE, > then it does not get "another" open, it gets "the same" open, but with > different access. When the client hold a write delegation, then it can > be sure there is only one open stateid for that file - the one that it > holds (it cannot hold two for the same file). >=20 > > The scenario I observed is that the requesting client held an OPEN > > for SHARED_ACCESS_READ on the file. The code in > > nfsd4_add_rdaccess_to_wrdeleg() assumes that if NFSD is about > > to set up a write delegation, the pointer in fi_fds[O_RDONLY] is NULL. > > That assumption isn=E2=80=99t true if that client still holds the S_A_R= OPEN > > state id, and fi_fds[O_RDONLY] for that file then gets overwritten and > > the nfsd_file it previously referenced is orphaned. >=20 > I agree that the current code is flawed. It needs to allow for the > possibility that the client already had the file open. I just don't see > the justification for withholding a delegation when an open is upgraded > from read-only to read-write. >=20 > If the client already holds a READ delegation, then I see that there > might be a problem. I don't think there *should* be a problem, but I > cannot see in the RFC how it would be handled. Would the existing > delegation get upgraded the same way that the OPEN stateid is upgraded?= =20 > Or would a new delegation be issued? The RFC isn't clear so I don't > think it can happen (safely). >=20 > I note that section 10.4 says: >=20 > The following is a typical set of conditions that servers might use > in deciding whether an OPEN should be delegated:=20 > .... > - There must be no current OPEN conflicting with the requested delega= tion. >=20 > That text seems advisory rather than normative. Does an OPEN from the > same client conflict with a delegation? Maybe it depends on your > perspective. >=20 > I also note 18.16.3 says: >=20 > If another client has a delegation of the file being opened that > conflicts with open being done (...), the delegation(s) MUST be > recalled, >=20 > So if the SAME client has a delegation - it doesn't need to be recalled? >=20 > and > In the case of an OPEN_DELEGATE_WRITE delegation, any open by a > different client will conflict, >=20 > Again "different client" - any open by the same client, it would seem, > does not conflict. >=20 I agree with Neil here (despite my questioning this on our call yesterday). Conceptually, granting a write delegation to a client that already holds an open stateid for the file doesn't seem problematic. Before returning that delegation, the client would need to establish open stateids for any opens that it had granted locally. If it already holds an open stateid though, then that isn't a problem IMO -- it just has a head start on establishing them before a DELEGRETURN. --=20 Jeff Layton