linux-kernel - Re: [RFC PATCH] pstore: Switch pmsg_lock to an rt

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Message-ID: <CANDhNCpFzG4sR1qcrWe+c=SzBfCMBm-Vv-50U4NTTC_awkto2Q@mail.gmail.com>
Date:   Wed, 14 Dec 2022 15:08:17 -0800
From:   John Stultz <jstultz@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Wei Wang <wvw@...gle.com>,
        Midas Chien <midaschieh@...gle.com>,
        "Connor O'Brien" <connoro@...gle.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>, kernel-team@...roid.com
Subject: Re: [RFC PATCH] pstore: Switch pmsg_lock to an rt_mutex to avoid
 priority inversion

On Wed, Dec 14, 2022 at 2:53 PM Kees Cook <keescook@...omium.org> wrote:
> On Mon, Dec 05, 2022 at 08:32:53PM +0000, John Stultz wrote:
> > Wei Wang reported seeing priority inversion caused latencies
> > caused by contention on pmsg_lock, and suggested it be switched
> > to a rt_mutex.
> >
> > I was initially hesitant this would help, as the tasks in that
> > trace all seemed to be SCHED_NORMAL, so the benefit would be
> > limited to only nice boosting.
> >
> > However, another similar issue was raised where the priority
> > inversion was seen did involve a blocked RT task so it is clear
> > this would be helpful in that case.
> >
> > Feedback would be appreciate!
>
> This looks fine to me. Is there an appropriate "Fixes:" tag that could
> be used?

Not other than the ~3.19 era original introduction of the pmsg.c file
where that mutex was introduced, I don't think.

But I'll respin with that.

thanks
-john