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 645BA130A73; Fri, 24 Jan 2025 15:31:27 +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=1737732688; cv=none; b=duEusmN+L8VJ/SdYFtv9Q3VC34fExRSMQjKlNsJ9Qv1zdjqMPTTEnxas0qqB2qruqthAqQTd9h+M/1Yh7iuxSoTpAs//M+g6fg+qnck4d4uIUKbqWuFjZ3sVLb4Ck/kjhd7XkPPqSZcld9pItUxmQbgvxOtdj2F++yeD+WCMKZ0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737732688; c=relaxed/simple; bh=vRsaEGdvkciLVRLRkt4MCf69aBeLvA7Pj7RCbgHp9hY=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=UGM1Gu1qZfT6DirYYeG6LLank0xJOlVB5Q5JCrHpbFbCWKiynkryUWysdpx7FuLqXrb3zVxavSvuLKBdnygSqXM3y9PjwUOVlEWwvCRodiBxEhnbYsP6YLwauxBr/Cdah73rahdKh+4K+ZSVDs6UjypT39vk3ANqGJSfRQEqkls= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a+KyVJFc; 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="a+KyVJFc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A52BC4CED2; Fri, 24 Jan 2025 15:31:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737732687; bh=vRsaEGdvkciLVRLRkt4MCf69aBeLvA7Pj7RCbgHp9hY=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=a+KyVJFcfcd4VUir9MGc6qdsOkLyk4dwrssAfs1D/6qD+58OK+aWb1k+VON6QLnnf 2UCxDOB+0tuURT2XujX6+PCGsntMwHLhed1HYY4WFW+BHb22dT3vW3f6GyXfhc7V28 0BaM5/mDTpoiEGZotC1UofruHLCGuW3AcyZWJLVpoHIyEXIpT4hVdvWmYxDOlpn9Zy bqp/R47+WNSn/tFw12LlbVHcEynTWK3NugD0bH/4BA32uOWnQDKN8yE3w1IIb0DhsQ EviDbRx3/lnsyuMVbIjLaAHPVqL0PEGjnBWmlboafawrMQ5dv9YfnYJnnIGe+IAZN6 s/stR17LsdL9A== Message-ID: <39a9a8e714b0cdf728080862a5fe69bbc617361e.camel@kernel.org> Subject: Re: [PATCH 7/8] nfsd: clean up and amend comments around nfsd4_cb_sequence_done() From: Jeff Layton To: Chuck Lever , Neil Brown , 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 Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Date: Fri, 24 Jan 2025 10:31:25 -0500 In-Reply-To: <1f967fd7-17b6-402e-ac55-aba956ba0d65@oracle.com> References: <20250123-nfsd-6-14-v1-0-c1137a4fa2ae@kernel.org> <20250123-nfsd-6-14-v1-7-c1137a4fa2ae@kernel.org> <8a6e1930-feee-47f8-8260-874b9c47f20e@oracle.com> <42ef9ff65c27fb7347f72e85b583ff74b2200bd6.camel@kernel.org> <1f967fd7-17b6-402e-ac55-aba956ba0d65@oracle.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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1/23/25 3:25 PM, Jeff Layton wrote: > > > > Add a new kerneldoc header, and clean up the comments a bit. > > >=20 > > > Usually I'm in favor of kdoc headers, but here, it's a static functio= n > > > whose address is not shared outside of this source file. The only > > > documentation need is the meaning of the return code, IMO. > > >=20 > >=20 > > If you like. I figured it wouldn't hurt to do a full kdoc comment. >=20 > Kdoc comments are pretty noisy. This one doesn't seem to me to add > much real value -- its callers are all right here in the same file. >=20 >=20 > > > > Signed-off-by: Jeff Layton > > > > --- > > > > fs/nfsd/nfs4callback.c | 26 ++++++++++++++++++++------ > > > > 1 file changed, 20 insertions(+), 6 deletions(-) > > > >=20 > > > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > > > > index 6e0561f3b21bd850b0387b5af7084eb05e818231..415fc8aae0f47c36f00= b2384805c7a996fb1feb0 100644 > > > > --- a/fs/nfsd/nfs4callback.c > > > > +++ b/fs/nfsd/nfs4callback.c > > > > @@ -1325,6 +1325,17 @@ static void nfsd4_cb_prepare(struct rpc_task= *task, void *calldata) > > > > rpc_call_start(task); > > > > } > > > > =20 > > > > +/** > > > > + * nfsd4_cb_sequence_done - process the result of a CB_SEQUENCE > > > > + * @task: rpc_task > > > > + * @cb: nfsd4_callback for this call > > > > + * > > > > + * For minorversion 0, there is no CB_SEQUENCE. Only restart the c= all > > > > + * if the callback RPC client was killed. For v4.1+ the error hand= ling > > > > + * is more sophisticated. > > >=20 > > > It would be much clearer to pull the 4.0 error handling out of this > > > function, which is named "cb_/sequence/_done". > > >=20 > > > Perhaps the need_restart label can be hoisted into nfsd4_cb_done() ? > > >=20 > >=20 > > If we do that then we'll need to change this function to return > > something other than a bool, and that's a larger change than I wanted > > to make here. I really wanted to keep these as small, targeted patches > > that can be backported easily. > >=20 > > I wouldn't object to further cleanup here on top of that though. >=20 > There's no reason to document the 4.0 logic if it's about to be moved > out. I strongly prefer making the code more self-documenting. Adding > a comment here about 4.0 then adding a patch on top moving the code > somewhere else seems silly to me. >=20 Ok. >=20 > > > > + * > > > > + * Returns true if reply processing should continue. > > > > + */ > > > > static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct= nfsd4_callback *cb) > > > > { > > > > struct nfs4_client *clp =3D cb->cb_clp; > > > > @@ -1334,11 +1345,11 @@ static bool nfsd4_cb_sequence_done(struct r= pc_task *task, struct nfsd4_callback > > > > 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. > > > > + * task was queued, 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 > > > > + * Note that if the callback connection is permanently lost, > > > > + * the submission code will error out. There is no need to > > > > * handle that case here. > > > > */ > > > > if (RPC_SIGNALLED(task)) > > > > @@ -1355,8 +1366,6 @@ static bool nfsd4_cb_sequence_done(struct rpc= _task *task, struct nfsd4_callback > > > > switch (cb->cb_seq_status) { > > > > case 0: > > > > /* > > > > - * No need for lock, access serialized in nfsd4_cb_prepare > > > > - * > > > > * RFC5661 20.9.3 > > > > * If CB_SEQUENCE returns an error, then the state of the slot > > > > * (sequence ID, cached reply) MUST NOT change. > > > > @@ -1365,6 +1374,11 @@ static bool nfsd4_cb_sequence_done(struct rp= c_task *task, struct nfsd4_callback > > > > ret =3D true; > > > > break; > > > > case -ESERVERFAULT: > > > > + /* > > > > + * Client returned NFS4_OK, but decoding failed. Mark the > > > > + * backchannel as faulty, but don't retransmit since the > > > > + * call was successful. > > > > + */ > > > > ++session->se_cb_seq_nr[cb->cb_held_slot]; > > > > nfsd4_mark_cb_fault(cb->cb_clp); > > > > break; > > >=20 > > > This old code abuses the meaning of ESERVERFAULT IMO. NFS4ERR_BADXDR = is > > > a better choice. But why call mark_cb_fault in this case? > > >=20 I can fix that up. BADXDR is more descriptive. > > > Maybe split this clean-up into a separate patch. > > >=20 > > >=20 > >=20 > > I'm only altering comments in this patch. Do you really want separate > > patches for the different comments? >=20 > Why call mark_cb_fault here? If NFSD retransmits this operation on a > fresh session/transport it will just fail to decode the reply again. >=20 > Do we believe that the decoding failure means there was a transport > problem of some kind? >=20 > It's clear we do not understand this code well enough to update the > existing comment, so my review comment above suggests a broader code > change is necessary. >=20 >=20 It won't be retransmitted in the ESERVERFAULT case. It just fails. I can't speak definitively, but my guess is that this is an extraordinary situation and the author (Kinglong Mee?) figured "might as well mark the cb faulty too". I don't think that's necessarily unreasonable, but I agree that it's unlikely to help. Unfortunately as the server in this situation, our options for alerting about callback problems are limited. Marking the CB channel as faulty isn't a great response, but it is at least something. The problem here is that these are callbacks, and if they fail, there is zero indication that there is a problem. Stepping back, when we do find failing callbacks, should we be doing more to alert the admin? What would be an appropriate response? Ratelimited pr_notice()? Conditional tracepoints? Something else? --=20 Jeff Layton