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 60880187553; Wed, 22 Jan 2025 15:44:45 +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=1737560686; cv=none; b=hzukE1WUJjyMpLGHpYpHkdhI8H8AdpbaSgTcWlvRC5lyyfJZMRCAaY57YS165OcpQJg/rgGI/NY7Yj2W1qsCNEZfG6RqZ0tfpTFgb53mMetFsXhPOLAs4Ibp0jGUUn/4SIpy4vecuhgtNljUBe43uMLpcG10gy6rgD+zHarlKkQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737560686; c=relaxed/simple; bh=p8idTzD8KFlG/b8mfoboFG4wbeZ1FzbVWgapto/q5+o=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=rEyXKeeFmvxbnWdX45kIYh7Ebj3HISs1FK/RVwoJ0ycYWG4piEHfRpt3LaF0nwIeyuYHrqg6ehARpgQkcNHsCSrEbzL7CXCcLt//JKUim6beQuDAR3l77qY3KqSvH0OWgbLcV0iZuSWaaVU2+iC/tuWabSixWZly3TUmMDGByQk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LKNucROz; 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="LKNucROz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F880C4CED2; Wed, 22 Jan 2025 15:44:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737560685; bh=p8idTzD8KFlG/b8mfoboFG4wbeZ1FzbVWgapto/q5+o=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=LKNucROztJEn8j3xao2zmcBsy26x4ems91wpbbC6NSD3rGroKMimEvHeVKx57b6Tc hA6nI0l5QSCt1ODwNxZesYkRLEXr4DMggSoZz/00+6l2ubN9CCVywHU1lii9hJfqej zocLn96UGJuIDPF3a/csHNZyFrybjust2FZwKfgj5bmRLJYpEyb1QX+u+EUzffYnMp d1p4MKgrkIjLb2eCv62fblSrfKWw1aj73TcUVE6OX8c2T43xWLj/B35omnrHfBLni8 U05HJVZ5/7AAq6AZ2zHvi6QJktlYEjH1Hvl3GVTxLoCO2eDxq+R1WudEC2IUaDM/qI y9Evu/vOm2YeQ== Message-ID: <6196ed07e6db1bf664d2f10280cbe0e80857583e.camel@kernel.org> Subject: Re: [PATCH] nfsd: always handle RPC_SIGNALLED earlier in nfsd4_cb_sequence_done() From: Jeff Layton To: Chuck Lever , Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 22 Jan 2025 10:44:43 -0500 In-Reply-To: References: <20250122-nfsd-6-14-v1-1-6e1fb49ac545@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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Layton wrote: > > The v4.0 client always restarts the callback when the connection is shu= t > > down (which is indicated by RPC_SIGNALLED()). The RPC is then requeued > > and the result eventually should complete (or be aborted). > >=20 > > The v4.1 code instead processes the result and only later decides to > > restart the call. Even more problematic is the fact that it releases th= e > > slot beforehand. The restarted call may get a new slot, which would > > could break DRC handling. >=20 > "break DRC handling" -- I'd like to understand this. >=20 > NFSD always sets cachethis to false in CB_SEQUENCE, so there is no DRC > for these operations. The only thing the client saves is the slot > sequence number IIUC. >=20 > Is retrying an uncached operation via a different slot a problem? >=20 Ahh, I missed that we always set cachethis to false. So, there is probably now a problem with the DRC after all. Still, I don't see a good argument for processing the CB_SEQUENCE result, when we intend to retransmit the call anyway. >=20 > > Change nfsd4_cb_sequence_done() such that RPC_SIGNALLED() is handled th= e > > same way irrespective of the minorversion. Check it early, before > > processing the CB_SEQUENCE result, and immediately restart the call. >=20 > It would be lovely to have some test cases that exercise the server's > backchannel retry logic. >=20 It sure would. I think that sort of thing would require a synthetic client (like pynfs). Since we're on the subject too, pynfs is broken on Fedora 41. That moved to python 3.13, which dropped support for the the xdrlib module. There is a forked xdrlib3 module which may be a suitable replacement, but I need to see if I can get it to work. >=20 > > Signed-off-by: Jeff Layton > > --- > > fs/nfsd/nfs4callback.c | 32 ++++++++++++++++---------------- > > 1 file changed, 16 insertions(+), 16 deletions(-) > >=20 > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > > index 50e468bdb8d4838b5217346dcc2bd0fec1765c1a..05afdf94c6478c7d698b059= fa33dd9e7af49b91e 100644 > > --- a/fs/nfsd/nfs4callback.c > > +++ b/fs/nfsd/nfs4callback.c > > @@ -1334,21 +1334,24 @@ static bool nfsd4_cb_sequence_done(struct rpc_t= ask *task, struct nfsd4_callback > > struct nfsd4_session *session =3D clp->cl_cb_session; > > bool ret =3D true; > > =20 > > - if (!clp->cl_minorversion) { > > - /* > > - * If the backchannel connection was shut down while this > > - * task was queued, we need to resubmit it after setting up > > - * a new backchannel connection. > > - * > > - * Note that if we lost our callback connection permanently > > - * the submission code will error out, so we don't need to > > - * handle that case here. > > - */ > > - if (RPC_SIGNALLED(task)) > > - goto need_restart; > > + /* > > + * If the backchannel connection was shut down while this > > + * task was queued, resubmit it after setting up a new backchannel > > + * connection. > > + * > > + * If the backchannel connection is permanently lost, the submission > > + * code will error out, so there is no need to handle that case here. > > + * > > + * For the v4.1+ case, do this without releasing the slot or doing > > + * any further processing. It's possible that the restarted call will > > + * be a retransmission of an earlier call to the server and that will > > + * help ensure that the DRC works correctly. > > + */ > > + if (RPC_SIGNALLED(task)) > > + goto need_restart; > > =20 > > + if (!clp->cl_minorversion) > > return true; > > - } > > =20 > > if (cb->cb_held_slot < 0) > > goto need_restart; > > @@ -1403,9 +1406,6 @@ static bool nfsd4_cb_sequence_done(struct rpc_tas= k *task, struct nfsd4_callback > > } > > trace_nfsd_cb_free_slot(task, cb); > > nfsd41_cb_release_slot(cb); > > - > > - if (RPC_SIGNALLED(task)) > > - goto need_restart; > > out: > > return ret; > > retry_nowait: > >=20 > > --- > > base-commit: a8acd0de47f22619d62d548b86bcfc9a4de2b2c6 > > change-id: 20250122-nfsd-6-14-77c1ad5d9f01 > >=20 > > Best regards, >=20 >=20 --=20 Jeff Layton