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 5BF8719BBA; Mon, 27 Jan 2025 15:43:40 +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=1737992620; cv=none; b=eevyO0hkaE9wx7epUsfHWTE4B1tZmxGjEagK5w0jQ5V6q9KjMZupCV22QXpdjI+JgVcbd0SFU9NUOJSuBqOFQy20JUxJZHJGUgI0xn4mBozzQzGzaA8Hea7Qf0N3KdexfY5KOUak+a9gO0wK6q1GNPq7EB3WQDyx5Ur/L0M8DAs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737992620; c=relaxed/simple; bh=FF4I//QwpAmKu9WdHqN0rUQlglUArDcAj5q6Sbnig7w=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=KTOSe3kPOKy24a4guVubkw8HfchPpLXPAv19wZn2K5dHjQaY1Yd8Hh5L06+wasr0htxRaQW4rRz6dr2KiBmwDVPvfkXjKWS536bAxz/17t4dzhulgoOWAVvA/w9eP917bvQOVB5p3YxcDlfiDYfhCHl+IO9hutXuXtG1MxF+v1Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=m55FTrc3; 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="m55FTrc3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B3A1FC4CED2; Mon, 27 Jan 2025 15:43:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737992620; bh=FF4I//QwpAmKu9WdHqN0rUQlglUArDcAj5q6Sbnig7w=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=m55FTrc3g3e/jyNJ5392HSIT7P3eg2/OMo6CkxNs3Sc2vqUCpwR+bVVzqMNGtmbxf BuP5hB7SM2ZVHK2pCX/Cp2fOdknvG2+key7S8tqpLgXyLcdHTmlKhV4zLbZUr7kaY5 vFeDSMy3Mu5LqxEhAdMjPsOTLwxuVUElA7o3p3NJ8Mql2okkz8pvhMn/JWKV31Dy+r 2kz0FZE+U0hCENBJOxqrQD/yIS6oOVlpoM57ry4nK6RYbd9U6ii23u9GMi7UB8Zwaa +AnUHl/oSNUpBlgjONr4VYO/asWMg+I9tUh9V0GtpTFt0bqKFFV9ImPIHM96DfeFe7 ldCxfgoFpChXA== Message-ID: <7bf69557c04b6c9084cdc153f30bd3ac7cb48065.camel@kernel.org> Subject: Re: [PATCH 1/8] nfsd: don't restart v4.1+ callback when RPC_SIGNALLED is set From: Jeff Layton To: Chuck Lever , NeilBrown Cc: Olga Kornievskaia , Dai Ngo , Tom Talpey , "J. Bruce Fields" , Kinglong Mee , Trond Myklebust , Anna Schumaker , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Date: Mon, 27 Jan 2025 10:43:37 -0500 In-Reply-To: References: <20250123-nfsd-6-14-v1-0-c1137a4fa2ae@kernel.org> <20250123-nfsd-6-14-v1-1-c1137a4fa2ae@kernel.org> <173784610046.22054.813567864998956753@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 VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ 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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 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2025-01-26 at 11:41 -0500, Chuck Lever wrote: > On 1/26/25 6:18 AM, Jeff Layton wrote: > > On Sun, 2025-01-26 at 10:01 +1100, NeilBrown wrote: > > > On Fri, 24 Jan 2025, Jeff Layton wrote: > > > > This is problematic, since the RPC might have been entirely success= ful. > > > > There is no point in restarting a v4.1+ callback just because > > > > RPC_SIGNALLED is true. The v4.1+ error handling has other mechanism= s for > > > > detecting when it should retransmit the RPC. > > >=20 > > > But why might RPC_SIGNALLED() ever be true? > > > The flag RPC_TASK_SIGNALLED is only ever set by rpc_signal_task() whi= ch > > > is only called from rpc_killall_tasks() and __rpc_execute() for > > > non-async tasks which doesn't apply to nfsd callbacks as they are > > > started with rpc_call_async(). > > >=20 > > > rpc_killall_tasks() is called by fs/nfs/ which isn't relevant for us, > > > and from rpc_shutdown_client(). In those cases we certainly don't wa= nt > > > the request to be retried, though the nfsd4_process_cb_update() case = is > > > a little interesting as we do want it to be retried, but in a differe= nt > > > client. > > >=20 > > > So the code you are removing is either dead code because something el= se > > > will prevent the restart when a client is being shut down, or it is b= ad > > > code because it would delay rpc_shutdown_client() while the request i= s > > > retried. > > >=20 > > > I haven't dug the extra step to figure out which, but either way I th= ink > > > the code should go. > >=20 > > Thanks. That was my analysis too. >=20 > Agreed, this code is problematic, but it appears to me that some of > these problems are not resolved by simply removing the signal check. >=20 >=20 > > rpc_shutdown_client() is called when we tear down and rebuild the > > rpc_client. nfsd does this in setup_callback_client(), which gets > > called from nfsd4_process_cb_update() (basically when we detect that > > the backchannel is having problems). > >=20 > > There are really only two states: We either got a reply from the server > > before the client went down, or we didn't. In the case where we got a > > reply, there is no need to retry anything. In the case where we didn't, > > the tk_status will be '1', so there is no need to check RPC_SIGNALLED() > > at all here. >=20 > Fwiw, the "cb_seq_status =3D=3D 1" arm skips the signal check in the curr= ent > code. >=20 >=20 > > The existing code could lead to the call being retried when we had > > already gotten a perfectly valid reply. >=20 > Here's a case-by-case audit: >=20 > - NFS_OK: SEQUENCE was decoded and passed sanity checks. So this should > not ever requeue in here. It might be requeued during subsequent > processing. >=20 > - ESERVERFAULT: SEQUENCE was decoded but failed sanity checking. The > reply should be dropped now, and the session marked FAULT. No requeue > is ever needed here. >=20 > [ I question whether the sequence number should be bumped in this > case -- the client's callback server replied with the identity of > some other slot. And anyway, this session is about to become > toast. ] >=20 It didn't necessarily reply with the ID of a different slot. It's just that the decoding failed in some way. It could have been any of the cases in decode_cb_sequence4resok(). Maybe that function needs to return more distinct error codes so we know what was mangled. > - 1: The timeout case. We want a fresh session here, so it falls > through to BADSESSION. >=20 Ok. > - NFS4ERR_BADSESSION: This needs a requeue so that the operation can > be retried with a fresh session. But it should always check if the > rpc_clnt is shutting down before doing so. This is a problem in the > current code. >=20 I'm not sure I understand the problem you see with that in the existing code. There's a rather complicated dance in nfsd4_process_cb_update(), but if the nfs4_client is shutting down, then clp->cl_cb_client will be NULL after it, and the callback will end. You said "rpc_clnt" though, so I'm not sure I understand the scenario you mean. > - NFS4ERR_DELAY: Skips the signal check, but shouldn't. If the rpc_clnt > is shutting down, this RPC should not be requeued. >=20 Good point -- ot sure how we deal with that in a non-racy way. I'll think about it. > - NFS4ERR_BAD_SLOT: Skips the signal check, but shouldn't. I need to > think more about BAD_SLOT recovery best practice. >=20 RPC_SIGNALLED() is irrelevant here. I think what we want to do is mark the backchannel as faulty, _leak_ the slot and retry via the workqueue (not just requeue the rpc_task). That should just cause the callback to exit once it runs again. We should also mark the backchannel as faulty, since the client and server no longer agree on the size of the slot table. > - NFS4ERR_SEQ_MISORDERED: Does one retry with a seq_nr of 1. It > probably should terminate if that fails. IMO this should check for > rpc_clnt shutdown before requeuing the retry. >=20 Fair enough. There is a frustrating lack of guidance in the spec about SEQ_MISORDERED. We should probably mark the BC as having a FAULT too if the retry fails. > - default: I don't think this case should ever be requeued, but it > appears that it could be if the rpc_clnt is shutting down. >=20 Yeah. Might not hurt to throw a pr_warn() here too. I think we never want to fall into this case. In any case, my intention is to fix up the cb_session lifetime problem first, and then we can rework the error handling from the callbacks on top of that. --=20 Jeff Layton