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 B6BA847ECDD; Tue, 1 Sep 2026 17:09:17 +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=1788282559; cv=none; b=ILbN/hlEHx++HiGSfd+VEUjlFSIlTaJVQwkq8Ob1f9/dQYTnjmQ74KqXPlgiu/LQytSP50/GjeNKgTTCpw6iOqL0R/icCRmoPjQ5XBCNpF5yf7+k5/azXeBwN4ZHDYO3BwmPHbFpl0pJ/LG7E6zfUMM+4GcXLdw/ZDImcxyDZAo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788282559; c=relaxed/simple; bh=QmIQi50CDRxkqFEhgMVEMoLmiC4RETD8fMqVnWWOHyc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Rt4sGPS4nAfbly6If2Ncgxdk+kBBsmZSN3d3jONW0PkqipNM7L6+/4DrYqsI4w/75eQaiJ83rCN/QywTdn6VLDqeiBjeYUL8hEtiYyZ1bHbfLcz6EAPopoj+ueieL6B0FUNR4t7fAEPxloJsrUaRmbolbvmgfRCiTdYraHcDzWU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HvpxBTQm; 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="HvpxBTQm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5DAB81F000E9; Tue, 1 Sep 2026 17:09:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788282557; bh=TGSn5dtg1waC38dglTeKDSErn0jwBarwcBAqBGsH7fQ=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=HvpxBTQmd04p8B5b9ziWGciNyT0WhO66aj21rRugBkf6N8jD0cfgepyMYhFE45ddt 3fYzNuddP/P0zI8yeEs0+YSo5nVsS/jW+lkCVSOtuwprQ4/mkeqB8WfblA/TNmK7dh BufVOt84sGB55M2hlwpqqlNqUHRR/bF1FvuKklqjlmVJ/6LHWLTyhS5ym20uhaQGkA 1VHnDqUFFf8AadR/nFF+UmGLygyYF8B2OAMTdGOj11ksefq2hUscT2lLsK1UJi0jdM 7QvQO+xdxBYXbjy8VBMy81Mf5skd2PF693vwwWm0hmNjC62C+clTudQwFL5OUdM/d6 qxtD9lPPyuJFg== Message-ID: <6cf26aa1e2a4b92e94d425a014427d2fd8da1367.camel@kernel.org> Subject: Re: [PATCH] nfsd: accept a backdated timestamp from a delegation holder From: Jeff Layton To: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: Thomas Haynes , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 01 Sep 2026 13:09:14 -0400 In-Reply-To: References: <20260901-delegts-v1-1-9937f7ee4370@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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9:09 AM, Jeff Layton wrote: > > A client with an attribute delegation reports the file times in a > > SETATTR at DELEGRETURN. nfsd ignores a time that moves backwards. It > > then stamps the c/mtime with the current time, so the file keeps the > > DELEGRETURN time. cp -p, rsync -t and tar -x lose timestamps. > >=20 > > The client applies an explicit utimensat() to its own inode. It sends n= o > > SETATTR while it holds the delegation, so the backdated value reaches > > nfsd only as TIME_DELEG_MODIFY. The client can send an RPC for each tim= e > > change instead. That also works, but it loses the caching that the > > delegation allows. > >=20 > > The delegation makes the client the authority for these times, so treat > > its SETATTR as a statement of fact. The client can set the same value > > with an ordinary SETATTR, which nfsd applies without a check. > >=20 > > - nfsd accepts a backwards atime or mtime. > > - An mtime that moves backwards sets the ctime to the current time. > > The ctime never moves backwards. > > - nfsd still clamps a future time. > > - The CB_GETATTR path keeps the old rule. A backwards time there shows > > a stale report. > >=20 > > RFC 9754 says that the server ignores a time before the original time. > > This patch does not follow that sentence. The same section also says > > that the server MUST accept the change or MUST reject it with > > NFS4ERR_DELAY. A silent discard does neither. A retry after > > NFS4ERR_DELAY carries the same backdated value, so that option cannot > > succeed. > >=20 > > There is still one gap: nfsd cannot tell an explicit utimensat() from a > > report of a write. An mtime after the delegation and before the current > > time therefore sets the ctime to that mtime, instead of to "now". RFC > > 9754 requires this. Fixing that would require the client to issue an RP= C > > for the mtime. > >=20 > > Fixes: 3952f1cbcbc4 ("nfsd: fix SETATTR updates for delegated timestamp= s") > > Signed-off-by: Jeff Layton > > Assisted-by: Claude:claude-opus-5 >=20 >=20 > Hi Jeff, LLM-generated review suggested the below finding is a blocker. >=20 > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c > > index bb74eef43938..fa3a43c20e95 100644 > > --- a/fs/nfsd/nfs4proc.c > > +++ b/fs/nfsd/nfs4proc.c >=20 > [ ... ] >=20 > > @@ -1302,21 +1315,23 @@ vet_deleg_attrs(struct nfsd4_setattr *setattr, = struct nfs4_delegation *dp) > > struct timespec64 now =3D current_time(dp->dl_stid.sc_file->fi_inode)= ; > > struct iattr *iattr =3D &setattr->sa_iattr; > > =20 > > - if ((setattr->sa_bmval[2] & FATTR4_WORD2_TIME_DELEG_ACCESS) && > > - !nfsd4_vet_deleg_time(&iattr->ia_atime, &dp->dl_atime, &now)) > > - iattr->ia_valid &=3D ~(ATTR_ATIME | ATTR_ATIME_SET); > > + if (setattr->sa_bmval[2] & FATTR4_WORD2_TIME_DELEG_ACCESS) > > + clamp_deleg_time(&iattr->ia_atime, &now); > > =20 > > if (setattr->sa_bmval[2] & FATTR4_WORD2_TIME_DELEG_MODIFY) { > > - if (nfsd4_vet_deleg_time(&iattr->ia_mtime, &dp->dl_mtime, &now)) { > > - iattr->ia_ctime =3D iattr->ia_mtime; > > - if (nfsd4_vet_deleg_time(&iattr->ia_ctime, &dp->dl_ctime, &now)) > > - dp->dl_setattr =3D true; > > - else > > - iattr->ia_valid &=3D ~(ATTR_CTIME | ATTR_CTIME_SET); > > - } else { > > - iattr->ia_valid &=3D ~(ATTR_CTIME | ATTR_CTIME_SET | > > - ATTR_MTIME | ATTR_MTIME_SET); > > - } > > + clamp_deleg_time(&iattr->ia_mtime, &now); > > + > > + /* > > + * The ctime must not move backwards. Carry the mtime into it > > + * only when that advances it; otherwise clear ATTR_CTIME_SET so > > + * that notify_change() stamps the ctime with the current time, > > + * which is what a local utimensat() would do. > > + */ > > + iattr->ia_ctime =3D iattr->ia_mtime; > > + if (!nfsd4_vet_deleg_time(&iattr->ia_ctime, &dp->dl_ctime, &now)) > ^^^^^^^^^^^^ >=20 > Is dp->dl_ctime the right value to compare against here? It is sampled > once, when the delegation is granted, and nothing refreshes it after > that: >=20 > fs/nfsd/nfs4state.c:nfs4_open_delegation() { > ... > dp->dl_atime =3D stat.atime; > dp->dl_ctime =3D stat.ctime; > dp->dl_mtime =3D stat.mtime; > ... > } >=20 > Is there anything that stops a client from sending more than one SETATTR > with TIME_DELEG_MODIFY while it holds the delegation? >=20 > Say the first one carries an mtime T5 that is later than dl_ctime. > nfsd4_vet_deleg_time() returns true, ATTR_CTIME_SET stays set, and the > inode ctime becomes T5. >=20 > If a second SETATTR then backdates the mtime to T3, where dl_ctime < T3 < > T5, the comparison is still against the grant-time dl_ctime. It returns > true again, so ATTR_CTIME_SET stays set and T3 is carried into ia_ctime. >=20 > notify_change() -> setattr_copy() -> inode_set_ctime_deleg() then drops > that update, because T3 is older than the T5 already in the inode: >=20 > fs/inode.c:inode_set_ctime_deleg() { > ... > /* If the update is older than the existing value, skip it. */ > if (timespec64_compare(&update, &cur_ts) <=3D 0) > return cur_ts; > ... > } >=20 > The mtime moves back to T3 and the ctime stays at T5, so the ctime is > neither carried from the mtime nor stamped with the current time. That > looks different from the comment just above it, and from the commit > message: "An mtime that moves backwards sets the ctime to the current > time." >=20 > Would comparing against the inode's current ctime work better here? The > inode is already in hand for the current_time() call at the top of the > function. >=20 >=20 Yes, I think we do want to rework it to do that. Additionally, I noticed another race condition that we ought to fix while we're in here. I'll be sending a v2, but I think we have to push some of this handling into the VFS layer so that it's done under more consistent locking and properly uses the mgtime infrastructure. --=20 Jeff Layton