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 EF3A2239E9A for ; Mon, 3 Nov 2025 19:40:06 +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=1762198807; cv=none; b=fo0byow2a0e/CKai4yJOdLjuwZs18Tg50rmbkf+q/joHDkQRnQLp3ixwdS/aVAIt15Auof4IPG0UHMaAXTCy2TrDEZjW9vcCHiIRaeQ6Mpec7GQwlbZjN4aLzMlNU2Ss+Oh2dTrRZatKgdUhlLfIJvjb7jMgypFiDEJb5FlyG5I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762198807; c=relaxed/simple; bh=LQtYdmOq73h8AfvTIxPcoK0dAJstUILPluaBELxRdxA=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Edx0TKQxYR9rX/3+B0TOveb5uXT4ycCEXzNnHomqjy3sR9jhD51fd6p28VNWZpC1llczD7XlYR9/dIF4zbIsrBPFWn4YVrrUf5sFFbABHB2Q01C4pUXLo98fKMKcF5ux4e1jGw0ROm9KpuebByxM+OUWLqJsw0fFXbYIYeMOL2o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=io0uQo0z; 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="io0uQo0z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D3ACAC4CEE7; Mon, 3 Nov 2025 19:40:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762198806; bh=LQtYdmOq73h8AfvTIxPcoK0dAJstUILPluaBELxRdxA=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=io0uQo0zlaV/0JXsYNoum7HJwuqN24OIKEbWfpevQlqnkSU3FXtV3+phCT0ip4Gpn a2kIph8ym5kPrrhwnW6ABtMIWS3w7f+oUZxFNddmq0cI1m7xO8GWPGGzvTfCIP6RLo JquJQyQP3OBPfqZwS6pkBgcVpMKHkQP3poyF4R0hvLZLRMBkkUY7DeB3YBe/FQzXlt WmnYEiW4A/kbQ+G+YnzrKXJZq932QMG5YStHGIIzv2CIis12P3o5j9QBNvquXodop1 LZXPUjYmJwebYmHhp9vbzkKSr+0yNzEMzsfAnqnYkvitxq2/DQQaHld+m8s+6mjEed 04o2JgRR7MusQ== Message-ID: <9553b72a3c54e264950f35bfd40abd5628ee6268.camel@kernel.org> Subject: Re: [PATCH 2/3] NFSD: Do not fence the client on NFS4ERR_RETRY_UNCACHED_REP error From: Jeff Layton To: Dai Ngo , Chuck Lever , Christoph Hellwig Cc: neilb@ownmail.net, okorniev@redhat.com, tom@talpey.com, linux-nfs@vger.kernel.org Date: Mon, 03 Nov 2025 14:40:04 -0500 In-Reply-To: References: <20251101185220.663905-1-dai.ngo@oracle.com> <20251101185220.663905-3-dai.ngo@oracle.com> <20251103114500.GC14852@lst.de> <841a3ef8-d5c8-4f87-9244-f79a10c66e3b@oracle.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Mon, 2025-11-03 at 11:36 -0800, Dai Ngo wrote: > On 11/3/25 11:22 AM, Jeff Layton wrote: > > On Mon, 2025-11-03 at 10:50 -0800, Dai Ngo wrote: > > > On 11/3/25 6:16 AM, Chuck Lever wrote: > > > > On 11/3/25 6:45 AM, Christoph Hellwig wrote: > > > > > On Sat, Nov 01, 2025 at 11:51:34AM -0700, Dai Ngo wrote: > > > > > > NFS4ERR_RETRY_UNCACHED_REP error means client has seen and repl= ied > > > > > > to the layout recall, no fencing is needed. > > > > > RFC 5661 specifies that error as: > > > > >=20 > > > > > The requester has attempted a retry of a Compound that it pre= viously > > > > > requested not be placed in the reply cache. > > > > >=20 > > > > > which to me doesn't imply a positive action here. > > > > Agreed, this status code seems like a loss of synchronization of se= ssion > > > > state between the client and server, or an implementation bug. Ie, = it > > > > seems to mean that at the very least, session re-negotiation is nee= ded, > > > > at first blush. Should the server mark a callback channel FAULT, fo= r > > > > instance? > > > >=20 > > > >=20 > > > > > But I'm not an > > > > > expert at reply cache semantics, so I'll leave others to correct = me. > > > > > But please add a more detailed comment and commit log as this is > > > > > completely unintuitive. > > > > The session state and the state of the layout are at two different > > > > and separate layers. Connect the dots to show that not fencing is > > > > the correct action and will result in recovery of full backchannel > > > > operation while maintaining the integrity of the file's content. > > > >=20 > > > > So IMHO reviewers need this patch description to provide: > > > >=20 > > > > - How this came up during your testing (and maybe a small reproduce= r) > > > >=20 > > > > - An explanation of why leaving the client unfenced is appropriate > > > >=20 > > > > - A discussion of what will happen when the server subsequently sen= ds > > > > another operation on this session slot > > > Here is the sequence of events that leads to NFS4ERR_RETRY_UNCACHED_R= EP: > > >=20 > > > 1. Server sends CB_LAYOUTRECALL with stateID seqid 2 > > > 2. Client replies NFS4ERR_NOMATCHING_LAYOUT > > > 3. Server does not receive the reply due to hard hang - no server thr= ead > > > available to service the reply (I will post a fix for this probl= em) > > > 4. Server RPC times out waiting for the reply, nfsd4_cb_sequence_done > > > is called with cb_seq_status =3D=3D 1, nfsd4_mark_cb_fault is ca= lled > > > and the request is re-queued. > > > 5. Client receives the same CB_LAYOUTRECALL with stateID seqid 2 > > > again and this time client replies with NFS4ERR_RETRY_UNCACHED_R= EP. > > >=20 > > > This process repeats forever from step 4. > > >=20 > > I'm a little confused here. I could see that you might not be able to > > process a LAYOUTRETURN if all nfsd threads were blocked waiting for the > > break_layout(), but I don't get why that would blocks a CB_LAYOUTRECALL > > reply. > >=20 > > For the server, CB_LAYOUTRECALL is a client RPC (server acts as client > > and vice versa). A CB_LAYOUTRECALL shouldn't depend on having a nfsd > > thread available, since it runs in the context of a workqueue thread. > >=20 > > What am I missing? >=20 > This is call stack when the server receives the callback reply: >=20 > receive_cb_reply+1 > svc_tcp_recvfrom+3531 > svc_handle_xprt+3747 > svc_recv+511 > nfsd+588 > kthread+916 > ret_from_fork+479 > ret_from_fork_asm+26 >=20 > As shown, it requires a NFSD thread to service it. The NFSD thread eventu= ally > calls xprt_complete_rqst to wake up the RPC task waiting for the reply. >=20 Thanks. That's the bit I was missing. I'll look forward to seeing your fix! --=20 Jeff Layton