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

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Message-ID: <20250710040607.GdzUE7A0@linutronix.de>
Date: Thu, 10 Jul 2025 06:06:07 +0200
From: Nam Cao <namcao@...utronix.de>
To: Xi Ruoyao <xry111@...111.site>
Cc: Christian Brauner <brauner@...nel.org>,
	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 Thu, Jul 10, 2025 at 05:48:08AM +0200, Nam Cao wrote:
> On Thu, Jul 10, 2025 at 11:08:18AM +0800, Xi Ruoyao wrote:
> > After upgrading my kernel to the recent mainline I've encountered some
> > stability issue, like:
> > 
> > - When GDM started gnome-shell, the screen often froze and the only
> > thing I could do was to switch into a VT and reboot.
> > - Sometimes gnome-shell started "fine" but then starting an application
> > (like gnome-console) needed to wait for about a minute.
> > - Sometimes the system shutdown process hangs waiting for a service to
> > stop.
> > - Rarely the system boot process hangs for no obvious reason.
> > 
> > Most strangely in all the cases there are nothing alarming in dmesg or
> > system journal.
> > 
> > I'm unsure if this is the culprit but I'm almost sure it's the trigger.
> > Maybe there's some race condition in my userspace that the priority
> > inversion had happened to hide...  but anyway reverting this patch
> > seemed to "fix" the issue.
> > 
> > Any thoughts or pointers to diagnose further?

I fetched Linus's tree, and noticed that the latest commit in Linus tree
fixes an use-after-free issue in eventpoll:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8c2e52ebbe885c7eeaabd3b7ddcdc1246fc400d2

Any chance it resolves your issue?

Nam