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 7763520FAAC; Fri, 21 Feb 2025 14:37:05 +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=1740148625; cv=none; b=HGRGl9ETxXzGFs+eb85ejXWD1bZeZy+AKq2LsLm7fDawfxzRjyO3UY+SlWjPR/yvha5on488v4M8PXZfvNZUdpNDuVZTvL3+8oTPizgOrUfSPzAMKbBozmsNB9qiw0oENGHH5/iDsTjxsJhcwN+k0T87Lbci5bUtvzkgCahNv+M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740148625; c=relaxed/simple; bh=4rvoSQ+7x8TqwO7+8ycb5v7yrOX5LPtCmwJL1bfA0V0=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=S3X0jCPwujSfs3sZjnJBm+vQMI4rtNfNbwveBJ4lJZ/6isOVe00u49IwjFXW0Fij3d0U3KwdeHxQPxONdUjpztQTlZewYpXkeOZ2KrGKtInfHVSbvU/U9qSFJ5vaT78oYo1c/qjzwYglWmmHS8et7NA4P4+ufiwBCKD6ZKagDD4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VmUPAHnC; 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="VmUPAHnC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B70FC4CEE8; Fri, 21 Feb 2025 14:37:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740148625; bh=4rvoSQ+7x8TqwO7+8ycb5v7yrOX5LPtCmwJL1bfA0V0=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=VmUPAHnCYfceBkf2BL5diRHWGzI6TvB7gkDjjG6+imsZZmsvpMBBJ//+agtm7LoQO T6iPqUDc5f4xwXVarMDv+QhHSqP0p3NqhQVZIEJ4k3ujkrPaFjQWrvHWQ2CTHIfal2 bwgBCp8tlpZAXuluEkjB4fdnh2jO+zDret85Z63cozXVyNSNxsjlzS8RfflzJMgPtf TML1fnTbwyuxq1Uso63MhXzsez/0qScY84KEsqR4dHhCuvXiVLxh6IBt1ZWJIDZyV7 r8aUXsrQ6vMJkZG5z0ulW0E55gwQh+mn2T/ATKCWo11qhnb9eqYuCaPU6McmtiCMml ZHS0l89/dMuNw== Message-ID: Subject: Re: [PATCH] nfsd: decrease cl_cb_inflight if fail to queue cb_work From: Jeff Layton To: Benjamin Coddington Cc: Chuck Lever , Li Lingfeng , neilb@suse.de, okorniev@redhat.com, Dai.Ngo@oracle.com, tom@talpey.com, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai1@huaweicloud.com, houtao1@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com, lilingfeng@huaweicloud.com Date: Fri, 21 Feb 2025 09:37:02 -0500 In-Reply-To: References: <20250218135423.1487309-1-lilingfeng3@huawei.com> <0ae8a05272c2eb8a503102788341e1d9c49109dd.camel@kernel.org> <04ed0c70b85a1e8b66c25b9ad4d0aa4c2fb91198.camel@kernel.org> <9cea3133-d17c-48c5-8eb9-265fbfc5708b@oracle.com> <8afc09d0728c4b71397d6b055dc86ab12310c297.camel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; 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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 Fri, 2025-02-21 at 09:06 -0500, Benjamin Coddington wrote: > On 18 Feb 2025, at 9:40, Jeff Layton wrote: >=20 > > On Tue, 2025-02-18 at 09:31 -0500, Chuck Lever wrote: > > > On 2/18/25 9:29 AM, Jeff Layton wrote: > > > > On Tue, 2025-02-18 at 08:58 -0500, Jeff Layton wrote: > > > > > On Tue, 2025-02-18 at 21:54 +0800, Li Lingfeng wrote: > > > > > > In nfsd4_run_cb, cl_cb_inflight is increased before attempting = to queue > > > > > > cb_work to callback_wq. This count can be decreased in three si= tuations: > > > > > > 1) If queuing fails in nfsd4_run_cb, the count will be decremen= ted > > > > > > accordingly. > > > > > > 2) After cb_work is running, the count is decreased in the exce= ption > > > > > > branch of nfsd4_run_cb_work via nfsd41_destroy_cb. > > > > > > 3) The count is decreased in the release callback of rpc_task = =E2=80=94 either > > > > > > directly calling nfsd41_cb_inflight_end in nfsd4_cb_probe_relea= se, or > > > > > > calling nfsd41_destroy_cb in . > > > > > >=20 > > > > > > However, in nfsd4_cb_release, if the current cb_work needs to r= estart, the > > > > > > count will not be decreased, with the expectation that it will = be reduced > > > > > > once cb_work is running. > > > > > > If queuing fails here, then the count will leak, ultimately cau= sing the > > > > > > nfsd service to be unable to exit as shown below: > > > > > > [root@nfs_test2 ~]# cat /proc/2271/stack > > > > > > [<0>] nfsd4_shutdown_callback+0x22b/0x290 > > > > > > [<0>] __destroy_client+0x3cd/0x5c0 > > > > > > [<0>] nfs4_state_destroy_net+0xd2/0x330 > > > > > > [<0>] nfs4_state_shutdown_net+0x2ad/0x410 > > > > > > [<0>] nfsd_shutdown_net+0xb7/0x250 > > > > > > [<0>] nfsd_last_thread+0x15f/0x2a0 > > > > > > [<0>] nfsd_svc+0x388/0x3f0 > > > > > > [<0>] write_threads+0x17e/0x2b0 > > > > > > [<0>] nfsctl_transaction_write+0x91/0xf0 > > > > > > [<0>] vfs_write+0x1c4/0x750 > > > > > > [<0>] ksys_write+0xcb/0x170 > > > > > > [<0>] do_syscall_64+0x70/0x120 > > > > > > [<0>] entry_SYSCALL_64_after_hwframe+0x78/0xe2 > > > > > > [root@nfs_test2 ~]# > > > > > >=20 > > > > > > Fix this by decreasing cl_cb_inflight if the restart fails. > > > > > >=20 > > > > > > Fixes: cba5f62b1830 ("nfsd: fix callback restarts") > > > > > > Signed-off-by: Li Lingfeng > > > > > > --- > > > > > > fs/nfsd/nfs4callback.c | 10 +++++++--- > > > > > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > > >=20 > > > > > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > > > > > > index 484077200c5d..8a7d24efdd08 100644 > > > > > > --- a/fs/nfsd/nfs4callback.c > > > > > > +++ b/fs/nfsd/nfs4callback.c > > > > > > @@ -1459,12 +1459,16 @@ static void nfsd4_cb_done(struct rpc_ta= sk *task, void *calldata) > > > > > > static void nfsd4_cb_release(void *calldata) > > > > > > { > > > > > > struct nfsd4_callback *cb =3D calldata; > > > > > > + struct nfs4_client *clp =3D cb->cb_clp; > > > > > > + int queued; > > > > > >=20 > > > > > > trace_nfsd_cb_rpc_release(cb->cb_clp); > > > > > >=20 > > > > > > - if (cb->cb_need_restart) > > > > > > - nfsd4_queue_cb(cb); > > > > > > - else > > > > > > + if (cb->cb_need_restart) { > > > > > > + queued =3D nfsd4_queue_cb(cb); > > > > > > + if (!queued) > > > > > > + nfsd41_cb_inflight_end(clp); > > > > > > + } else > > > > > > nfsd41_destroy_cb(cb); > > > > > >=20 > > > > > > } > > > > >=20 > > > > > Good catch! > > > > >=20 > > > > > Reviewed-by: Jeff Layton > > > > >=20 > > > >=20 > > > > Actually, I think this is not quite right. It's a bit more subtle t= han > > > > it first appears. The problem of course is that the callback workqu= eue > > > > jobs run in a different task than the RPC workqueue jobs, so they c= an > > > > race. > > > >=20 > > > > cl_cb_inflight gets bumped when the callback is first queued, and o= nly > > > > gets released in nfsd41_destroy_cb(). If it fails to be queued, it'= s > > > > because something else has queued the workqueue job in the meantime= . > > > >=20 > > > > There are two places that can occur: nfsd4_cb_release() and > > > > nfsd4_run_cb(). Since this is occurring in nfsd4_cb_release(), the = only > > > > other option is that something raced in and queued it via > > > > nfsd4_run_cb(). > > >=20 > > > What would be the "something" that raced in? > > >=20 > >=20 > > I think we may be able to get there via multiple __break_lease() calls > > on the same layout or delegation. That could mean multiple calls to the > > ->lm_break operation on the same object. >=20 > Sorry for the late response, but isn't ->lm_break() already serialized in > __break_lease for the same file_lease? We don't call lm_break(fl) if > lease_breaking(fl). >=20 lease_breaking() is only checked when want_write is false. IOW, if you're breaking the lease for write, then lm_break is always called. Is that a bug or a feature? I'm not sure, but it's been that way since ~2011. --=20 Jeff Layton