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 123AA1E4AE; Sat, 25 Jan 2025 22:04:26 +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=1737842667; cv=none; b=jvGn2gcYnOm/BxYARtusqVVYMnAm9AxCRiWlQcFEd/3BlvlXb5JmGJq/HOelCZmM3ThDvqTRu49NCuNcDEsorW1hkKal6Kn3eHzzEcQKAoHpkFaGk3f/VkR38AAo1H5WIoL33gpuKd/jcqvX8TrYtZ9UAYnbIwP7t344Ch7fEBA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737842667; c=relaxed/simple; bh=J8CwoHDew2ch8hbII+qFLFuRR6imAQksihwTwo9lBe8=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=cFIAqhTzLQy8d69Qdjzjtws3J1EBn4q1UkQGTfO6kwx+Th0PyIWp97xUmTWxCyqsPiY+ZD9at5Vr33xLnXGBppsDyRRWnrK53khHZNp2FDwDXOTmPlAc28MOLPSqpF8CKA6cleWWo6GJTt424Os79/JanVlMvuRfrmwoRlmeBrs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QnXny65P; 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="QnXny65P" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68362C4CED6; Sat, 25 Jan 2025 22:04:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737842666; bh=J8CwoHDew2ch8hbII+qFLFuRR6imAQksihwTwo9lBe8=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=QnXny65P2n7gsECmITir410K9YdwC3vHcvJ2v2hKYMta2MwoD9A/hKhVXCJtVVCNK OVrryhnq4PTJAZuPeerqc9MZdwW/H8k6gV9MzndkcJhP+Ey+cm9N2iVOu561RdxLkl oZxX4NcuA4Dj2LxEFp/SxYaqFerSh1IwwpOtU0LEH8QiA1XeYk0yWZWGWTxROx+AAj J9LV2hmaM+YTgy8jUCsAW7ZSB35ZKfOlEGzLsa0jphyMkxBZklegLaAz4bhlv5OZ41 CXbrn5TVgZ4o+5U2Ha/6WXFasg5v4Iq2pp/hk4wP5av1FYvdMaEu7e+LigiDJKTWQ4 Ijf/W+8mk/1+A== Message-ID: Subject: Re: [PATCH 1/8] nfsd: don't restart v4.1+ callback when RPC_SIGNALLED is set 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: Sat, 25 Jan 2025 17:04:23 -0500 In-Reply-To: <421c33ce-d43b-4444-a83a-a25f4fabfce2@oracle.com> References: <20250123-nfsd-6-14-v1-0-c1137a4fa2ae@kernel.org> <20250123-nfsd-6-14-v1-1-c1137a4fa2ae@kernel.org> <421c33ce-d43b-4444-a83a-a25f4fabfce2@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 YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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DfX/sn9XcfoVZIxMpCRE750zvJvcCUz9HojsrMQ1NFc7MFT1z3MOW2/RlzPcog7xvR5ENPH19ojRD 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-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sat, 2025-01-25 at 11:24 -0500, Chuck Lever wrote: > On 1/23/25 3:25 PM, Jeff Layton wrote: > > This is problematic, since the RPC might have been entirely successful. > > There is no point in restarting a v4.1+ callback just because > > RPC_SIGNALLED is true. The v4.1+ error handling has other mechanisms fo= r > > detecting when it should retransmit the RPC. > >=20 > > Fixes: 7ba6cad6c88f ("nfsd: New helper nfsd4_cb_sequence_done() for pro= cessing more cb errors") > > Signed-off-by: Jeff Layton > > --- > > fs/nfsd/nfs4callback.c | 3 --- > > 1 file changed, 3 deletions(-) > >=20 > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > > index 50e468bdb8d4838b5217346dcc2bd0fec1765c1a..e12205ef16ca932ffbcc86d= 67b0817aec2436c89 100644 > > --- a/fs/nfsd/nfs4callback.c > > +++ b/fs/nfsd/nfs4callback.c > > @@ -1403,9 +1403,6 @@ static bool nfsd4_cb_sequence_done(struct rpc_tas= k *task, struct nfsd4_callback > > } > > trace_nfsd_cb_free_slot(task, cb); > > nfsd41_cb_release_slot(cb); > > - > > - if (RPC_SIGNALLED(task)) > > - goto need_restart; > > out: > > return ret; > > retry_nowait: > >=20 >=20 > I too am skeptical about this logic, but I don't entirely understand it > yet. More importantly, though, I don't recall seeing (mis)behavior that > I can directly attribute to it, so I can't yet confirm or deny your=20 > assertion that "This is problematic". >=20 I haven't seen behavior that I can directly attribute to this either, but we have seen a number of strange panics and weird behaviors in the callback code over the years that may be related. At this point, I think you're correct that we will probably need to do more than just small, incremental changes here. =20 > Before making a code change here, let's gather a little evidence of a > real problem. For instance, we might want to replace this logic with > something better rather than wholesale removing it. >=20 > You might start by enabling aggressive disconnect injection to see how > backchannel recovery works (or that it doesn't work!). I'm trying this > on my kdevops NFSD while running fstests: >=20 > cd /sys/kernel/debug/fail_sunrpc/ > echo Y > ignore-cache-wait > echo Y > ignore-client-disconnect > echo 24847 > interval > echo 97 > times > echo 100 > probability >=20 >=20 Unfortunately, I've found an even bigger problem in the callback code. It accesses the clp->cl_cb_session pointer when processing the call and reply, but that pointer doesn't imply a reference and nothing else ensures that the nfsd4_session object will stick around while this happens. I think a callback can race with a DESTROY_SESSION and cause a UAF. I started working on patches to fix this up, but it's a bit complex and will take some time. Please don't apply any of these until I get a better picture of what will need to be changed. Stay tuned! --=20 Jeff Layton