linux-kernel - Re: [PATCH v3] eventpoll: Fix priority inversion problem

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Message-ID: <20250714-leumund-sinnen-44309048c53d@brauner>
Date: Mon, 14 Jul 2025 10:59:58 +0200
From: Christian Brauner <brauner@...nel.org>
To: Nam Cao <namcao@...utronix.de>, 
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Xi Ruoyao <xry111@...111.site>, 
	Frederic Weisbecker <frederic@...nel.org>, Valentin Schneider <vschneid@...hat.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, John Ogness <john.ogness@...utronix.de>, 
	Clark Williams <clrkwllms@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, 
	linux-rt-users@...r.kernel.org, Joe Damato <jdamato@...tly.com>, 
	Martin Karsten <mkarsten@...terloo.ca>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v3] eventpoll: Fix priority inversion problem

On Fri, Jul 11, 2025 at 11:50:08AM +0200, Nam Cao wrote:
> On Fri, Jul 11, 2025 at 11:44:28AM +0200, Christian Brauner wrote:
> > I think we should revert the fix so we have time to fix it properly
> > during v6.17+. This patch was a bit too adventurous for a fix in the
> > first place tbh.
> 
> Agreed. I did feel a bit uneasy when I saw the patch being applied to
> vfs.fixes.

I was on the fence myself and I juggled the commit between vfs.fixes and
vfs-6.17.misc because I wasn't sure whether we should consider such
priority inversion fix something that's urgent or not.

I tried to communicate to Linus that I was uncertain about this
particular patch at the beginning of

https://lore.kernel.org/20250704-vfs-fixes-fa31f5ff8c05@brauner

But I should've called it earlier.

Linus, thanks for reverting this! I had a revert ready as announced on
Friday for today but it's good that this got kicked out already.

My lesson from this is that touching epoll without a really really good
and urgent reason always end up a complete mess. So going forward we'll
just be very careful here.