linux-kernel - Re: v5.14-rc3-rt1 losing wakeups?

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Message-ID: <20210802070218.5js3exubjxvsicx6@linutronix.de>
Date:   Mon, 2 Aug 2021 09:02:18 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mike Galbraith <efault@....de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: v5.14-rc3-rt1 losing wakeups?

On 2021-08-01 17:14:49 [+0200], Mike Galbraith wrote:
> On Sun, 2021-08-01 at 05:36 +0200, Mike Galbraith wrote:
> > On Fri, 2021-07-30 at 22:49 +0200, Thomas Gleixner wrote:
> > > >
> > > > First symptom is KDE/Plasma's task manager going comatose.  Notice soon
> > >
> > > KDE/Plasma points at the new fangled rtmutex based ww_mutex from
> > > Peter.
> >
> > Seems not.  When booting KVM box with nomodeset, there's exactly one
> > early boot ww_mutex lock/unlock, ancient history at the failure point.
> 
> As you've probably already surmised given it isn't the ww_mutex bits,
> it's the wake_q bits.  Apply the below, 5.14-rt ceases to fail.  Take
> perfectly healthy 5.13-rt, apply those bits, and it instantly begins
> failing as 5.14-rt had been.

Given what you have replied to the locking thread/
ww_mutex_lock_interruptible() may I assume that the wake_q bits are fine
and it is just the ww_mutex?

Sebastian