From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 13F503F0755 for ; Tue, 7 Jul 2026 11:13:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783422827; cv=none; b=rv54NvVoS929ikQgRmbDEa2HtFH97qwt3hrdcy/XXKZTznSK16mtSFfSvcsts6EV20cmK8WoNuhpI0AnvfkRJB1IEb7SzlZF9Fa00ZU9rN0iMA9VhxtGUB0oxItUYbGXtJetMgi60fFur0ZIGdRS4hlAUu9y6a16e6K4zcpo46E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783422827; c=relaxed/simple; bh=Dzu7rnVWesWO7NYpJiNTRGrZ89JkEeuDSeGMgkecpuQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=svcjoE/vb+NlWeul05oAPAnP8GPgRSEoupyBe2rih6ex64l1WvDIcA4JDH1SkqsVW7pILVImw+GHnlfOIZHuPUyCxF+WnM6h+d8UsNTb3912aiImYgn1MAKA6xcCyO/n6O+q+tTIyT2baFVYEkl9U2UNcevcugpm9Ea5z80h7hI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Mi33wM6o; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Mi33wM6o" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 44EC91F000E9; Tue, 7 Jul 2026 11:13:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783422825; bh=Bw0/XH4zfsGmjY/LLIM7qPl1ckZCZWlnh+SL9ztqd/0=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=Mi33wM6oD+25fhW/baeE62loyH43lIFSdRk9iVK33pl0QrvUB83IGw4P9xmf8L08O 0QSupdki08Kfv72YXgc9HHIzjW0M0c3tv5bxJj+7dgmkTTMMcV2+dNZxZuPIlwCJnb HQHCaPoKq0ugbN1L2+Bne52iypLYzNyyQVAODHPTgYuLoVXRiDC005GwbiDxAksqH5 VLrLF7WMBWPPktG7t3aMMt8RcgjcFH7nwyRWksMSOINEjk4kgY7t6K4W2U/lmzpbtr SzDTOE2IwjtAKKly4ggQZxvBfgJklW+uMmIihbxMPBxdn1IVkSBQtDnRztCdtEiiaC pgyTf7Q+HbB9g== Message-ID: <817fa5902f35305b2c4f38b11379dbf6eade49c6.camel@kernel.org> Subject: Re: [PATCH v2 06/14] nfsd: in nfsd4_create_file() let VFS report if file was created. From: Jeff Layton To: NeilBrown Cc: Chuck Lever , Olga Kornievskaia , Dai Ngo , Tom Talpey , linux-nfs@vger.kernel.org Date: Tue, 07 Jul 2026 07:13:44 -0400 In-Reply-To: <178338050586.27465.16700298229223579148@noble.neil.brown.name> References: <20260705222032.1240057-1-neilb@ownmail.net> <20260705222032.1240057-7-neilb@ownmail.net> <8ef43a6cfb235b0ef449388d56a4faeab492160c.camel@kernel.org> <178338050586.27465.16700298229223579148@noble.neil.brown.name> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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DfX/sn9XcfoVZIxMpCRE750zvJvcCUz9HojsrMQ1NFc7MFT1z3MOW2/RlzPcog7xvR5ENPH19ojRD CHqumUHRry+RF0lH00clzX/W8OrQJZtoBPXv9ahka/Vp7kEulcBJr1cH5Wz/WprhsIM7U9pse1f1g Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-07-07 at 09:28 +1000, NeilBrown wrote: > On Tue, 07 Jul 2026, Jeff Layton wrote: > > On Mon, 2026-07-06 at 08:19 +1000, NeilBrown wrote: > > > From: NeilBrown > > >=20 > > > nfsd4_create_file() currently assumes that if a lookup failed but the= n a > > > create succeeds, then the "create" operation actually created the fil= e. > > > With atomic_open this may not be the case - some other actor might ha= ve > > > created the file between the lookup and the create. > > >=20 > > > So we move the call to nfsd4_vfs_create() earlier and set ->op_create= d > > > based on the FMODE_CREATED flag that it set. Then use "! ->op_creat= ed" > > > to trigger nfserr_exist handling. > > >=20 > > > The switch statement is split up into two if() statements. > > > First we check for the possibility of a successful exclusive > > > create and set ->op_create to true if appropriate. > > > Then we check for NFS4_CREATE_UNCHECKED to decide if a > > > pre-existing file means an error or success. > > >=20 > > > This allows us to combine the two fh_compose() calls to one place. > > >=20 > > > A subtle difference here is that we now must only pass O_EXCL to > > > dentry_create() for NFS4_CREATE_GUARDED. For the EXCLUSIVE create mo= des > > > we want a successful open even if the file already exists. We then > > > check the verifier after the open succeeded to see if it was exclusiv= e. > > >=20 > >=20 > > Do we really want a successful open in the EXCLUSIVE cases? > >=20 > > Opens have side effects (notably, that they can cause delegation > > recalls). If you have two racing clients creating a file, the first > > gets an open and write delegation and then the second ends up > > immediately causing a delegrecall for the first, even though it may > > never touch the file again after the OPEN fails. > >=20 > > I think we may want to reconsider that logic, if possible: Maybe we > > should keep using O_EXCL in those cases and just re-drive the open > > without it if it fails and the verifier looks right? That's a bit > > uglier, but that may cause fewer delegation recalls. >=20 > Thanks for raising this. My thinking was that next EXCLUSIVE creates > was weird. > If the server is re-exporting NFS, then think about what happens to the > verifier stored on the backend server. > First the verifier from the intermediate server is stored,=20 > then the nfs client on the intermediate server sends a SETATTR to remove = it,=20 > then the intermediate server sets the verifier from the originating > client. > then the originating client removes it. >=20 > So 4 setattrs altogether. >=20 > Also if the intermediate server ever gets a retransmit of the OPEN > request, it will send an EXCLUSIVE open to the backend server which will > fail even if the verifier is still correct. >=20 > I agree that recalling a delegation needlessly is not good, but will it > happen often? If the app checks for then name before trying the O_EXCL > open, then the delegation would not get recalled because the OPEN > wouldn't be tried. I wonder how often that happens.... >=20 > I think setting O_EXCL in the NFS4_CREATE_GUARDED case is important. > I'm open to discussion around the issues with O_EXCL and the > NFS4_CREATE_EXCLUSIVE case. >=20 > Maybe doing a lookup first when the exported fs is NFS would be an OK > compromise. >=20 I guess it shouldn't happen often, since we do check d_really_is_negative() prior to calling nfsd4_vfs_create(). Given that, let's go with the scheme you've got here. We can always revisit it if this turns out to be more of an issue. --=20 Jeff Layton