netdev - Re: [PATCH v13 0/9] ref_tracker: add ability to register a debugfs file for a ref_tracker

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Message-ID: <0c0e8c720705d86b37a103346bccc36de4f5b025.camel@kernel.org>
Date: Wed, 04 Jun 2025 08:32:29 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, "David S. Miller"	
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni	
 <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Maarten Lankhorst	
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Jani Nikula	
 <jani.nikula@...ux.intel.com>, Joonas Lahtinen
 <joonas.lahtinen@...ux.intel.com>,  Rodrigo Vivi <rodrigo.vivi@...el.com>,
 Tvrtko Ursulin <tursulin@...ulin.net>, Krzysztof Karas	
 <krzysztof.karas@...el.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, Qasim
 Ijaz	 <qasdev00@...il.com>, Nathan Chancellor <nathan@...nel.org>, Andrew
 Lunn	 <andrew@...n.ch>, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, 	dri-devel@...ts.freedesktop.org,
 intel-gfx@...ts.freedesktop.org, Thomas Weißschuh
 <thomas.weissschuh@...utronix.de>
Subject: Re: [PATCH v13 0/9] ref_tracker: add ability to register a debugfs
 file for a ref_tracker_dir

On Tue, 2025-06-03 at 19:29 -0700, Jakub Kicinski wrote:
> On Tue, 03 Jun 2025 07:27:11 -0400 Jeff Layton wrote:
> > For those just joining in, this series adds a new top-level
> > "ref_tracker" debugfs directory, and has each ref_tracker_dir register a
> > file in there as part of its initialization. It also adds the ability to
> > register a symlink with a more human-usable name that points to the
> > file, and does some general cleanup of how the ref_tracker object names
> > are handled.
> > 
> > This reposting is mostly to address Krzysztof's comments. I've dropped
> > the i915 patch, and rebased the rest of the series on top.
> > 
> > Note that I still see debugfs: warnings in the i915 driver even when we
> > gate the registration of the debugfs file on the classname pointer being
> > NULL. Here is a CI report from v12:
> > 
> >     https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_148490v8/bat-arls-6/igt@i915_selftest@live@workarounds.html
> > 
> > I think the i915 driver is doing something it shouldn't with these
> > objects. They seem to be initialized more than once, which could lead
> > to leaked ref_tracker objects. It would be good for one of the i915
> > maintainers to comment on whether this is a real problem.
> 
> I still see the fs crashes:
> https://netdev-3.bots.linux.dev/vmksft-packetdrill-dbg/results/149560/2-tcp-slow-start-slow-start-app-limited-pkt/stderr
> I'll hide this series from patchwork for now. We will pull from Linus
> on Thu, I'll reactivate it and let's see if the problem was already
> fixed.

Sorry, I never got any mail about those failures. I would have looked
at that sooner. It looks like the last netns reference can be put in a
rcu callback? That makes sense.

I think ref_tracker_dir_exit() has to remain safe to call from any
context. Perhaps we can defer the dentry deletion to the system_wq?

We can drop this series for now. I'll have to think about this.

Thanks,
-- 
Jeff Layton <jlayton@...nel.org>