linux-kernel - Re: [PATCH] Revert "seqlock: lockdep assert non-preemptibility on seqcount

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Message-ID: <15863.1597822443@turing-police>
Date:   Wed, 19 Aug 2020 03:34:03 -0400
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Mark Starovoytov <mstarovoitov@...vell.com>,
        Igor Russkikh <irusskikh@...vell.com>,
        "David S. Miller" <davem@...emloft.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        linux-kernel@...r.kernel.org, mingo@...hat.com, paulmck@...nel.org,
        peterz@...radead.org, rostedt@...dmis.org, tglx@...utronix.de,
        will@...nel.org
Subject: Re: [PATCH] Revert "seqlock: lockdep assert non-preemptibility on seqcount_t write"

On Wed, 19 Aug 2020 09:00:22 +0200, Sebastian Andrzej Siewior said:
> On 2020-08-18 17:56:49 [-0700], Guenter Roeck wrote:
> > Nice catch. FWIW, there is no obvious reason why this would need to be atomic.
> > The calling code does not set a lock, meaning there can be two (or more)
> > callers entering this code. Weird, especially since the code looks like it
> > would actually need a mutex to work correctly. It might be interesting to
> > see what happens if there are, say, half a dozen scripts/processes trying
> > to read the hwmon attribute introduced by this patch at the same time.
>
> => https://lkml.kernel.org/r/20200818161439.3dkf6jzp3vuwmvvh@linutronix.de

Looks reasonable to me, though I've not verified that it's preemptible at that
point...

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