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 29701243397; Sun, 9 Feb 2025 02:14:29 +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=1739067270; cv=none; b=QhVukv/uKVWpOxwVdR4HX0euPIJpk+oTWPuP9AhXl7NCUMT6YwqV1ymZa0/WRaicn0h+D8QPditWSEXfwxEYFm20/Vs9I4LvsOelNXzNI9bJRTGUj87tBgx7XKautLTjVrhrGR41BnsF3iwjGCdSUUPgrHGzWHo9QFN6rP6gR4k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739067270; c=relaxed/simple; bh=+5VPMaYkNSCw3GauppovCB4+LCvmyrzzvLshGOlr29I=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=PMQTAdqD/u2rbU5DxDFURoDw/dxte8R7qZg7cNjL3E41w3g8FBpH6O0aS/VzCstsLrH+ZP+UHrj/t7phVnZxdVJo6u++7686P01pRKAFAXg/NNP3C3rGuR3MeghPLtua6wDPvnKhGMt7LsQWIhi91mbYE3uDYsaNU4jdZoXnFZk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=niiLaXvo; 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="niiLaXvo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2A2CC4CED6; Sun, 9 Feb 2025 02:14:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739067269; bh=+5VPMaYkNSCw3GauppovCB4+LCvmyrzzvLshGOlr29I=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=niiLaXvoyGSiKbexpxDBhjkb2ebW5R67P0vw4oijBK20ODBlH7zsQsOXmvYh6jQ0H hfM5lptDtzzedyXinQOoTClwye7rUcGg3Uc3tHvc1reA35XCbjGyDnsPTy477k8YUR 0iJmTobc7iK70GD0uQG2aGyYpiiP9tUuuTLip8N38W7//75TPMH42V3TjRV6xRUrB1 YS+A7nQxp9DSh/WmQbUTL5aAzS6D90HBDCB/PW8fV6sp2qCnKl4YxtlGEqvOk6Z0vN cshIGAimQTDscRxpJaghdpXNfiJTYmdgiVN/Je6AEXJUpy8xzVto3m1FH1cxxZPa2p rWAJAfqcdRh0A== Message-ID: 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 21:14:27 -0500 In-Reply-To: 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> <35cae0eb73781bb36c49aed2c2bc49a808698635.camel@kernel.org> <2f9fe86f-b49c-460c-bf2e-fed97970952d@oracle.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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Lever wrote: > > On 2/8/25 3:45 PM, Jeff Layton wrote: > > > On Sat, 2025-02-08 at 14:18 -0500, Tom Talpey wrote: > > > > On 2/8/2025 11:08 AM, Jeff 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 o= f 1, and 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/nfs4callbac= k.c > > > > > > > > > index 10067a34db3afff8d4e4383854ab9abd9767c2d6..d6e3e8bb2= efabadda9f922318880e12e1cb2c23f 100644 > > > > > > > > > --- a/fs/nfsd/nfs4callback.c > > > > > > > > > +++ b/fs/nfsd/nfs4callback.c > > > > > > > > > @@ -1393,6 +1393,16 @@ static bool nfsd4_cb_sequence_done= (struct 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 we= re me, I'd > > > > > > > > remove it. Is there a "why" statement that could be made he= re? Like, > > > > > > > > why retry with a seq_nr of 1 instead of just failing immedi= ately? > > > > > > > >=20 > > > > > > >=20 > > > > > > > There isn't one that I know of. It looks like Kinglong Mee ad= ded it in > > > > > > > 7ba6cad6c88f, but there is no real mention of that in the cha= ngelog. > > > > > > >=20 > > > > > > > TBH, I'm not enamored with this remedy either. What if the se= q_nr was 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 a= nd sent 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 retr= y. 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 fun= ctional > > > > > > 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 caus= e the > > > > > client to (eventually) send a DESTROY_SESSION and create a new on= e. > > > > >=20 > > > > > Unfortunately, in the meantime, because of the way the callback c= hannel > > > > > update works, the server can end up trying to send the callback a= gain > > > > > 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 arm= ed > > > > to prevent runaway retries. > > > >=20 > > > > It's maybe worth considering what state the peer might be in when t= his > > > > happens. It too may effectively leak a slot, and if is retaining so= me > > > > bogus state either as a result of or because of the previous exchan= ge(s) > > > > then this may lead to future hangs/failures. Not pretty, and maybe = not > > > > worth trying to guess. > > > >=20 > > > > Tom. > > > >=20 > > >=20 > > >=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. > > >=20 > > > 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? > > >=20 > > > Either way, I'd consider that to be follow-on work to this set. > >=20 > > As a general comment, I think making a heroic effort to recover in any > > of these cases is probably not worth the additional complexity. Where i= t > > is required or where we believe it is worth the trouble, that's where w= e > > want a detailed comment. > >=20 > > What we want to do is ensure forward progress. I'm guessing that error > > conditions are going to be rare, so leaking the slot until a certain > > portion of them are gone, and then indicating a session fault to force > > the client to start over from scratch, is probably the most > > straightforward approach. > >=20 > > So, is there a good reason to retry? There doesn't appear to be any > > reasoning mentioned in the commit log or in nearby comments. >=20 > Agreed on the general comment. >=20 > As for the "any reason to retry" - maybe. If it's a transient error we > don't want to give up early. Unfortunately that appears to be an > ambiguous situation, because SEQ_MISORDERED is allowed in place of > ERR_DELAY. I don't have any great suggestion however. >=20 IMO, we should retry callbacks (basically) indefinitely, unless the NFSv4 client is being torn down (i.e. lease expires or an unmount happened, etc). > Jeff, to your point that the "client should figure out something is > wrong", I'm not sure how you think that will happen. If the server is > making a delegation recall and the client receive code chooses to reject= =20 > it at the sequence check, how would that eventually cause the client to > reestablish the session (on the forechannel)? >=20 >=20 In the BADSLOT case, it calls nfsd4_mark_cb_fault(cb->cb_clp), which sets a flag in the client that makes it set SEQ4_STATUS_BACKCHANNEL_FAULT in the next SEQUENCE call. The client should take that as an indication that there is a problem and reestablish a new session (and maybe a new connection). Granted, it might take up to the next lease renewal, but there's not much else we can do if the client won't talk to us. That's why I was suggesting that we might time out the backchannel calls after two lease periods. OTOH, maybe it's sufficient to not queue any callbacks for courtesy clients? > >=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 sync > > > > > > > > > @@ -1403,12 +1413,6 @@ static bool nfsd4_cb_sequence_done= (struct 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 > >=20 > >=20 >=20 --=20 Jeff Layton