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 AD4C4267B72; Thu, 13 Mar 2025 13:52:03 +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=1741873923; cv=none; b=g/EfHNk/J/HGIOn/6unDz+5+R0t85qcf+omCdpFdfrU19ryH7G4e/eNDxOVd7wQay91w5iE05hGb6HWjOp/OOr9zmWl1AuKA3rVn9TtcXNIsNzbwTzwS5N2b2AwGIJnAkljT0Yx+E5+FD+5wRwLkUQnXYE/nURvRo+nVuUV6kLY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741873923; c=relaxed/simple; bh=xoyDodBFvNvmguT9IBaqx5WxLExGYaUZYbOSWw3WeAM=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=aqZjVBTvAipbhOwrtnk60aXPk0VkJyeGyAubHbmzt2c2uZUOmGjIk6UN0U1D7xysBikv+bmIkCFrYEEEZ6Cw8AbMIZNJ3PBRDGBirFOIyRneeMujluoG8iKhKLiyLSd6ojF0rMqkHErA0U0qA7UIkpxK/0wgRjTHiOd5CdKeWRA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fNFd9PbY; 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="fNFd9PbY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B7502C4CEE5; Thu, 13 Mar 2025 13:52:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1741873923; bh=xoyDodBFvNvmguT9IBaqx5WxLExGYaUZYbOSWw3WeAM=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=fNFd9PbYSlwvHXAweFPAWZH/AlJ7aS+fI5fv019D2PSu/qe+5Im8XZ3K2gEW1dkQI 7fs5toLr7n0RzbFWto2De6njD2bAWxSlDFJBz3BvUgdK3As5ealFp5C0gJVqd4ud/9 Yx5jrIZ0SK7kBq1aqJWG30HIbgmBJo5rHSsnBdUWLc0vqJ9l7gG+1qRbHVaEb3uEW8 xmH3BatLLr03NnoI3hMESgXZj4tQ+v2ONnWLtqKHP6pEk1cDCb3Ge5oER8daaHjoL9 DyJhJR6Fzd5FF0PsTnX1eyYD05+3cypQ4P4FuCUheVFqaVHjuqnZeFW0y1gbankVY6 tdeiZAvDBQNxA== Message-ID: Subject: Re: [PATCH] sunrpc: add a rpc_clnt shutdown control in debugfs From: Jeff Layton To: Benjamin Coddington Cc: Trond Myklebust , anna@kernel.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 13 Mar 2025 09:52:01 -0400 In-Reply-To: <0E1E14E2-BD4B-433B-8355-EEF45384BE83@redhat.com> References: <20250312-rpc-shutdown-v1-1-cc90d79a71c2@kernel.org> <7906109F-91D2-4ECF-B868-5519B56D2CEE@redhat.com> <997f992f951bd235953c5f0e2959da6351a65adb.camel@kernel.org> <8bf55a6fb64ba9e21a1ec8c5644355ffd6496c6e.camel@hammerspace.com> <0E1E14E2-BD4B-433B-8355-EEF45384BE83@redhat.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2025-03-13 at 09:35 -0400, Benjamin Coddington wrote: > On 13 Mar 2025, at 9:15, Jeff Layton wrote: >=20 > > On Wed, 2025-03-12 at 22:31 +0000, Trond Myklebust wrote: > > > On Wed, 2025-03-12 at 10:37 -0400, Jeff Layton wrote: > > > > On Wed, 2025-03-12 at 09:52 -0400, Benjamin Coddington wrote: > > > > > On 12 Mar 2025, at 9:36, Jeff Layton wrote: > > > > >=20 > > > > > > There have been confirmed reports where a container with an NFS > > > > > > mount > > > > > > inside it dies abruptly, along with all of its processes, but t= he > > > > > > NFS > > > > > > client sticks around and keeps trying to send RPCs after the > > > > > > networking > > > > > > is gone. > > > > > >=20 > > > > > > We have a reproducer where if we SIGKILL a container with an NF= S > > > > > > mount, > > > > > > the RPC clients will stick around indefinitely. The orchestrato= r > > > > > > does a MNT_DETACH unmount on the NFS mount, and then tears down > > > > > > the > > > > > > networking while there are still RPCs in flight. > > > > > >=20 > > > > > > Recently new controls were added[1] that allow shutting down an > > > > > > NFS > > > > > > mount. That doesn't help here since the mount namespace is > > > > > > detached from > > > > > > any tasks at this point. > > > > >=20 > > > > > That's interesting - seems like the orchestrator could just reord= er > > > > > its > > > > > request to shutdown before detaching the mount namespace.=C2=A0 N= ot an > > > > > objection, > > > > > just wondering why the MNT_DETACH must come first. > > > > >=20 > > > >=20 > > > > The reproducer we have is to systemd-nspawn a container, mount up a= n > > > > NFS mount inside it, start some I/O on it with fio and then kill -9 > > > > the > > > > systemd running inside the container. There isn't much the > > > > orchestrator > > > > (root-level systemd) can do to at that point other than clean up > > > > what's > > > > left. > > > >=20 > > > > I'm still working on a way to reliably detect when this has happene= d. > > > > For now, we just have to notice that some clients aren't dying. > > > >=20 > > > > > > Transplant shutdown_client() to the sunrpc module, and give it = a > > > > > > more > > > > > > distinct name. Add a new debugfs sunrpc/rpc_clnt/*/shutdown kno= b > > > > > > that > > > > > > allows the same functionality as the one in /sys/fs/nfs, but at > > > > > > the > > > > > > rpc_clnt level. > > > > > >=20 > > > > > > [1]: commit d9615d166c7e ("NFS: add sysfs shutdown knob"). > > > > > >=20 > > > > > > Signed-off-by: Jeff Layton > > > > >=20 > > > > > I have a TODO to patch Documentation/ for this knob mostly to wri= te > > > > > warnings > > > > > because there are some potential "gotchas" here - for example you > > > > > can have > > > > > shared RPC clients and shutting down one of those can cause > > > > > problems for a > > > > > different mount (this is true today with the > > > > > /sys/fs/nfs/[bdi]/shutdown > > > > > knob).=C2=A0 Shutting down aribitrary clients will definitely bre= ak > > > > > things in > > > > > weird ways, its not a safe place to explore. > > > > >=20 > > > >=20 > > > > Yes, you really do need to know what you're doing. 0200 permissions > > > > are > > > > essential for this file, IOW. Thanks for the R-b! > > >=20 > > > Sorry, but NACK! We should not be adding control mechanisms to debugf= s. > > >=20 > >=20 > > Ok. Would adding sunrpc controls under sysfs be more acceptable? I do > > agree that this is a potential footgun, however. It would be nicer to > > clean this situation up automagically. > >=20 > > > One thing that might work in situations like this is perhaps to make > > > use of the fact that we are monitoring whether or not rpc_pipefs is > > > mounted. So if the mount is containerised, and the orchestrator > > > unmounts everything, including rpc_pipefs, we might take that as a hi= nt > > > that we should treat any future connection errors as being fatal. > > >=20 > >=20 > > rpc_pipefs isn't being mounted at all in the container I'm using. I > > think that's not going to be a reliable test for this. > >=20 > > > Otherwise, we'd have to be able to monitor the root task, and check i= f > > > it is still alive in order to figure out if out containerised world h= as > > > collapsed. > > >=20 > >=20 > > If by the root task, you mean the initial task in the container, then > > that method seems a little sketchy too. How would we determine that > > from the RPC layer? > >=20 > > To be clear: the situation here is that we have a container with a veth > > device that is communicating with the outside world. Once all of the > > processes in the container exit, the veth device in the container > > disappears. The rpc_xprt holds a ref on the netns though, so that > > sticks around trying to retransmit indefinitely. > >=20 > > I think what we really need is a lightweight reference on the netns. > > Something where we can tell that there are no userland tasks that care > > about it anymore, so we can be more aggressive about giving up on it. > >=20 > > There is a "passive" refcount inside struct net, but that's not quite > > what we need as it won't keep the sunrpc_net in place. > >=20 > > What if instead of holding a netns reference in the xprt, we have it > > hold a reference on a new refcount_t that lives in sunrpc_net? Then, we > > add a pre_exit pernet_ops callback that does a shutdown_client() on all > > of the rpc_clnt's attached to the xprts in that netns. The pre_exit can > > then just block until the sunrpc_net refcount goes to 0. > >=20 > > I think that would allow everything to be cleaned up properly? >=20 > Do you think that might create unwanted behaviors for a netns that might > still be repairable? Maybe that doesn't make a lot of sense if there ar= e no > processes in it, but I imagine a network namespace could be in this state > and we'd still want to try to use it. >=20 I don't think so. Once there are no userland tasks holding a reference to a namespace, there is no way to reach it from outside the kernel, AFAICT, so there is no way repair it. It would actually be nice if we had a way to say "open net namespace with this inode number". I guess we could add filehandle and open_by_handle_at() support to nsfs... > which, if used, creates an explicit requirement for the orchestrator to > define exactly what should happen if the veth goes away. When creating t= he > namespace, the orchestrator should insert a rule that says "when this vet= h > disappears, we shutdown this fs". > > Again, I'm not sure if that's even possible, but I'm willing to muck arou= nd > a bit and give it a try. >=20 I'd really prefer to do something that "just works" with existing userland applications, but if we have to do something like that, then so be it. --=20 Jeff Layton