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 8A54F199B8; Wed, 29 Jan 2025 15:01:52 +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=1738162912; cv=none; b=hRyXtTvBpbpEmk2MatEkONlxfTl72+C9KmLLwFbeiJ/vyBqwNCm5IXzYRZkKR6Klg3UHD2BDu6siAUzJnJKdnmhGlAtZeI+keHM2KQqI9hPnsqnamJOn93FIry9OljHijF0NoHRiE3DITjXcZuz93puL2t3dQWWqPXumEI671gA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738162912; c=relaxed/simple; bh=FZK/pnGNMkDVIhbB5xWjy0PhrcIiQPlzg2J7f+yQZUM=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=qFv/hcPN2WS+kI0s5cUKhhkq/QI2g892yICWkhk3BuimZYgtwQ20uWEaM/8lGQqXKEwqvHTCj3u3bRqewax8vOOXwp5LpWYQ1OzysB5V/QiPg5X00aHq/bN6KjW8f3wx4jPzCEsUK5VG7CIEb9wzo9gHCTRNpsPfeo91H7b2jSM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=N/GbYdmC; 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="N/GbYdmC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0C726C4CED1; Wed, 29 Jan 2025 15:01:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738162912; bh=FZK/pnGNMkDVIhbB5xWjy0PhrcIiQPlzg2J7f+yQZUM=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=N/GbYdmC+cJHflkXgsRu+giPgslyE/Q1zXG/lOxDNZp2OO7uPNNDpihaBEJzxEVEW m+2Rv5QGh9/ioeS+G15+/b1R+urE1WXz26/xcV4cg9bae//a2bRBhhaE5I5R5iPUjm okSrReA2TR1FOibkfvqZYoa/BHTAmjfH3A8qvRD+hWEIeLJ71WNEzFQjF9BRY5aEx4 DBLatt24JpIzt/OxzKFW82mn8T1cZh6m+loZK1KgqvuGnoMz+DfwP/1eINbLT5TH3L UDyxdylsD+hj7nlIt/vtaAL/O2a0365ehEFcUPvEGa2p6Wy5IYh9WypHAAKy/Li5cJ PFnUh0BycwK+Q== Message-ID: <0722b556a8b01ca4f99e5d3ac5285efc666d69ec.camel@kernel.org> Subject: Re: [PATCH v2 0/7] nfsd: CB_SEQUENCE error handling fixes and cleanups From: Jeff Layton To: "J. Bruce Fields" Cc: Chuck Lever , Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Kinglong Mee , Trond Myklebust , Anna Schumaker , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 29 Jan 2025 10:01:49 -0500 In-Reply-To: References: <20250129-nfsd-6-14-v2-0-2700c92f3e44@kernel.org> <5760673a9adc597c1b235dd6a1670ed801d2feb1.camel@kernel.org> 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-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2025-01-29 at 09:40 -0500, J. Bruce Fields wrote: > On Wed, Jan 29, 2025 at 09:27:02AM -0500, Jeff Layton wrote: > > On Wed, 2025-01-29 at 09:21 -0500, J. Bruce Fields wrote: > > > On Wed, Jan 29, 2025 at 08:39:53AM -0500, Jeff Layton wrote: > > > > While looking over the CB_SEQUENCE error handling, I discovered tha= t > > > > callbacks don't hold a reference to a session, and the > > > > clp->cl_cb_session could easily change between request and response= . > > > > If that happens at an inopportune time, there could be UAFs or weir= d > > > > slot/sequence handling problems. > > >=20 > > > Nobody should place too much faith in my understanding of how any of > > > this works at this point, but.... My vague memory is that a lot of > > > things are serialized simply by being run only on the cl_callback_wq. > > > Modifying clp->cl_cb_session is such a thing. > >=20 > > It is, but that doesn't save us here. The workqueue is just there to > > submit jobs to the RPC client. Once that happens they are run via > > rpciod's workqueue (and in parallel with one another since they're > > async RPC calls). > >=20 > > So, it's possible that while we're waiting for a response from one > > callback, another is submitted, and that workqueue job changes the > > clp->cl_cb_session. >=20 > I think it calls rpc_shutdown_client() before changing > clp->cl_cb_session. >=20 It does, but the cl_cb_session doesn't carry a reference. My worry was that the client could call a DESTROY_SESSION at any time. Now that I look though, you may be right that that's enough to ensure it because nfsd4_destroy_session() calls nfsd4_probe_callback_sync() before putting the session reference. Still, that is a lot of reliance on these things happening in a particular order. > (Though I'm not sure whether rpc_shutdown_client guarantees that all rpc > processing for the client is completed before returning?) >=20 FWIW, it does wait for them to be killed: while (!list_empty(&clnt->cl_tasks)) { rpc_killall_tasks(clnt); wait_event_timeout(destroy_wait, list_empty(&clnt->cl_tasks), 1*HZ); } I'm not crazy about the fact that it does that synchronously in the workqueue job, but I guess not much else can be happening with callbacks until this completes. > --b. >=20 > >=20 > > Thanks for taking a look, Bruce! > >=20 > > >=20 > > > > This series changes the nfsd4_session to be RCU-freed, and then add= s a > > > > new method of session refcounting that is compatible with the old. > > > > nfsd4_callback RPCs will now hold a lightweight reference to the se= ssion > > > > in addition to the slot. Then, all of the callback handling is swit= ched > > > > to use that session instead of dereferencing clp->cb_cb_session. > > > > I've also reworked the error handling in nfsd4_cb_sequence_done() > > > > based on review comments, and lifted the v4.0 handing out of that > > > > function. > > > >=20 > > > > This passes pynfs, nfstests, and fstests for me, but I'm not sure h= ow > > > > much any of that stresses the backchannel's error handling. > > > >=20 > > > > These should probably go in via Chuck's tree, but the last patch to= uches > > > > some NFS cnd sunrpc client code, so it'd be good to have R-b's or A= -b's > > > > from Trond and/or Anna on that one. > > > >=20 > > > > Signed-off-by: Jeff Layton > > > > --- > > > > Changes in v2: > > > > - make nfsd4_session be RCU-freed > > > > - change code to keep reference to session over callback RPCs > > > > - rework error handling in nfsd4_cb_sequence_done() > > > > - move NFSv4.0 handling out of nfsd4_cb_sequence_done() > > > > - Link to v1: https://lore.kernel.org/r/20250123-nfsd-6-14-v1-0-c11= 37a4fa2ae@kernel.org > > > >=20 > > > > --- > > > > Jeff Layton (7): > > > > nfsd: add routines to get/put session references for callback= s > > > > nfsd: make clp->cl_cb_session be an RCU managed pointer > > > > nfsd: add a cb_ses pointer to nfsd4_callback and use it inste= ad of clp->cb_cb_session > > > > nfsd: overhaul CB_SEQUENCE error handling > > > > nfsd: remove unneeded forward declaration of nfsd4_mark_cb_fa= ult() > > > > nfsd: lift NFSv4.0 handling out of nfsd4_cb_sequence_done() > > > > sunrpc: make rpc_restart_call() and rpc_restart_call_prepare(= ) void return > > > >=20 > > > > fs/nfs/nfs4proc.c | 12 ++- > > > > fs/nfsd/nfs4callback.c | 212 ++++++++++++++++++++++++++++++++= ------------ > > > > fs/nfsd/nfs4state.c | 43 ++++++++- > > > > fs/nfsd/state.h | 6 +- > > > > fs/nfsd/trace.h | 6 +- > > > > include/linux/sunrpc/clnt.h | 4 +- > > > > net/sunrpc/clnt.c | 7 +- > > > > 7 files changed, 210 insertions(+), 80 deletions(-) > > > > --- > > > > base-commit: a05af3c6103b703d1d38d8180b3ebbe0a03c2f07 > > > > change-id: 20250123-nfsd-6-14-b0797e385dc0 > > > >=20 > > > > Best regards, > > > > --=20 > > > > Jeff Layton > >=20 > > --=20 > > Jeff Layton --=20 Jeff Layton