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 8B0621F3B89; Sat, 8 Feb 2025 20:45:53 +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=1739047553; cv=none; b=L6w5OGoMbcLiADMxw/Skv2k7G2OT/wUsZZr5oj8mE7UA0K3u6zTPJKelvr7eU/8R01y3yA3VomB1hvb2tZe30xdO+jFPpJphtBmavWvLmcJLt999IG00eYvMzsq8ZbkLJJB6UqSB31wq7hLegt4GT+bfz0qYfrpfsPxj4F2ifaM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739047553; c=relaxed/simple; bh=Zao7m8sPs2R+b8IWOgxr5W1kxZHjntdxauxRdT5uF8Y=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=QxSuoUbKGhd/XhidzbinjTESCL0e4syBuRB1cGP+FKwBVdP2HCB4GEsNi4ewrB9R71A78c4Orv2onln147aIngR5GriTQ+dNSJo6oF+Yb76JFyVOpImxyq4bU4TGWuME8ETCdqbbTQD6h1GN9ZAOCT8QxHRXluqD7WbRLIrkmH0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=I12+tXUw; 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="I12+tXUw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 45845C4CED6; Sat, 8 Feb 2025 20:45:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739047553; bh=Zao7m8sPs2R+b8IWOgxr5W1kxZHjntdxauxRdT5uF8Y=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=I12+tXUw+oyzpDLPemuaG+kmibOvLzlQr96BROh+48c3rNFZCkX2dhcaOp+Jxl14q Fcn8sBQwkwKq/w78+kc8Sq0KzU7Pz1vHL5+L3ncUnMwrUq7JaZXxuI7I4srsvV66Za vr59IVvJwN+HoHCNAKhH4fDTXbeRsqaA0VxTrur0I2cXW0Pgp7HANNg10YX+7eEFKL MXJsuKCvVCIcMZlDMrUrNVl0zI7Y0FJlqzijRCCZjjZwRjpIPddrnC10xCO3QndsM6 N54cbAb7kkEn1/QAMeHL0OKwevepmTU8VVi1Ta/n/wR0vVAH/ype+iDpseLeiE+naP aKsl/TE2+LoBA== Message-ID: <35cae0eb73781bb36c49aed2c2bc49a808698635.camel@kernel.org> Subject: Re: [PATCH v5 6/7] nfsd: handle CB_SEQUENCE NFS4ERR_SEQ_MISORDERED error better From: Jeff Layton To: Tom Talpey , Chuck Lever , Neil Brown , Olga Kornievskaia , Dai Ngo , "J. Bruce Fields" Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Sat, 08 Feb 2025 15:45:51 -0500 In-Reply-To: <29e739f1-2d85-40c2-a549-5ab9d71686b0@talpey.com> References: <20250207-nfsd-6-14-v5-0-f3b54fb60dc0@kernel.org> <20250207-nfsd-6-14-v5-6-f3b54fb60dc0@kernel.org> <28174296-129d-4459-aa23-a94bbf00d257@oracle.com> <3e4d14075482489cd010e4ea621c0bd368700e27.camel@kernel.org> <40970e33-4689-4623-a423-b346e739ba80@talpey.com> <66532654ca25280ffa30168a977601ba4a37aaab.camel@kernel.org> <29e739f1-2d85-40c2-a549-5ab9d71686b0@talpey.com> 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: > > On Sat, 2025-02-08 at 13:40 -0500, Tom Talpey wrote: > > > On 2/8/2025 10:02 AM, Jeff Layton wrote: > > > > On Sat, 2025-02-08 at 12:01 -0500, Chuck Lever wrote: > > > > > On 2/7/25 4:53 PM, Jeff Layton wrote: > > > > > > For NFS4ERR_SEQ_MISORDERED, do one attempt with a seqid of 1, a= nd then > > > > > > fall back to treating it like a BADSLOT if that fails. > > > > > >=20 > > > > > > Signed-off-by: Jeff Layton > > > > > > --- > > > > > > fs/nfsd/nfs4callback.c | 16 ++++++++++------ > > > > > > 1 file changed, 10 insertions(+), 6 deletions(-) > > > > > >=20 > > > > > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > > > > > > index 10067a34db3afff8d4e4383854ab9abd9767c2d6..d6e3e8bb2efabad= da9f922318880e12e1cb2c23f 100644 > > > > > > --- a/fs/nfsd/nfs4callback.c > > > > > > +++ b/fs/nfsd/nfs4callback.c > > > > > > @@ -1393,6 +1393,16 @@ static bool nfsd4_cb_sequence_done(struc= t rpc_task *task, struct nfsd4_callback > > > > > > goto requeue; > > > > > > rpc_delay(task, 2 * HZ); > > > > > > return false; > > > > > > + case -NFS4ERR_SEQ_MISORDERED: > > > > > > + /* > > > > > > + * Reattempt once with seq_nr 1. If that fails, treat this > > > > > > + * like BADSLOT. > > > > > > + */ > > > > >=20 > > > > > Nit: this comment says exactly what the code says. If it were me,= I'd > > > > > remove it. Is there a "why" statement that could be made here? Li= ke, > > > > > why retry with a seq_nr of 1 instead of just failing immediately? > > > > >=20 > > > >=20 > > > > There isn't one that I know of. It looks like Kinglong Mee added it= in > > > > 7ba6cad6c88f, but there is no real mention of that in the changelog= . > > > >=20 > > > > TBH, I'm not enamored with this remedy either. What if the seq_nr w= as 2 > > > > when we got this error, and we then retry with a seq_nr of 1? Does = the > > > > server then treat that as a retransmission? > > >=20 > > > So I assume you mean the requester sent seq_nr 1, saw a reply and sen= t a > > > subsequent seq_nr 2, to which it gets SEQ_MISORDERED. > > >=20 > > > If so, yes definitely backing up the seq_nr to 1 will result in the > > > peer considering it to be a retransmission, which will be bad. > > >=20 > >=20 > > Yes, that's what I meant. > >=20 > > > > We might be best off > > > > dropping this and just always treating it like BADSLOT. > > >=20 > > > But, why would this happen? Usually I'd think the peer sent seq_nr X > > > before it received a reply to seq_nr X-1, which would be a peer bug. > > >=20 > > > OTOH, SEQ_MISORDERED is a valid response to an in-progress retry. So, > > > how does the requester know the difference? > > >=20 > > > If treating it as BADSLOT completely resets the sequence, then sure, > > > but either a) the request is still in-progress, or b) if a bug is > > > causing the situation, well it's not going to converge on a functiona= l > > > session. > > >=20 > >=20 > > With this patchset, on BADSLOT, we'll set SEQ4_STATUS_BACKCHANNEL_FAULT > > in the next forechannel SEQUENCE on the session. That should cause the > > client to (eventually) send a DESTROY_SESSION and create a new one. > >=20 > > Unfortunately, in the meantime, because of the way the callback channel > > update works, the server can end up trying to send the callback again > > on the same session (and maybe more than once). I'm not sure that > > that's a real problem per-se, but it's less than ideal. > >=20 > > > Not sure I have a solid suggestion right now. Whatever the fix, it > > > should capture any subtlety in a comment. > > >=20 > >=20 > > At this point, I'm leaning toward just treating it like BADSLOT. > > Basically, mark the backchannel faulty, and leak the slot so that > > nothing else uses it. That allows us to send backchannel requests on > > the other slots until the session gets recreated. >=20 > Hmm, leaking the slot is a workable approach, as long as it doesn't > cascade more than a time or two. Some sort of trigger should be armed > to prevent runaway retries. >=20 > It's maybe worth considering what state the peer might be in when this > happens. It too may effectively leak a slot, and if is retaining some > bogus state either as a result of or because of the previous exchange(s) > then this may lead to future hangs/failures. Not pretty, and maybe not > worth trying to guess. >=20 > Tom. >=20 The idea here is that eventually the client should figure out that something is wrong and reestablish the session. Currently we don't limit the number of retries on a callback. Maybe they should time out after a while? If we've retried a callback for more than two lease periods, give up and log something? Either way, I'd consider that to be follow-on work to this set. > >=20 > > > >=20 > > > > Thoughts? > > > >=20 > > > > >=20 > > > > > > + if (session->se_cb_seq_nr[cb->cb_held_slot] !=3D 1) { > > > > > > + session->se_cb_seq_nr[cb->cb_held_slot] =3D 1; > > > > > > + goto retry_nowait; > > > > > > + } > > > > > > + fallthrough; > > > > > > case -NFS4ERR_BADSLOT: > > > > > > /* > > > > > > * BADSLOT means that the client and server are out of syn= c > > > > > > @@ -1403,12 +1413,6 @@ static bool nfsd4_cb_sequence_done(struc= t rpc_task *task, struct nfsd4_callback > > > > > > nfsd4_mark_cb_fault(cb->cb_clp); > > > > > > cb->cb_held_slot =3D -1; > > > > > > goto retry_nowait; > > > > > > - case -NFS4ERR_SEQ_MISORDERED: > > > > > > - if (session->se_cb_seq_nr[cb->cb_held_slot] !=3D 1) { > > > > > > - session->se_cb_seq_nr[cb->cb_held_slot] =3D 1; > > > > > > - goto retry_nowait; > > > > > > - } > > > > > > - break; > > > > > > default: > > > > > > nfsd4_mark_cb_fault(cb->cb_clp); > > > > > > } > > > > > >=20 > > > > >=20 > > > > >=20 > > > >=20 > > >=20 > >=20 >=20 --=20 Jeff Layton