linux-kernel - Re: [RFC PATCH 09/10] powerpc: snapshot thread flags

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Date:   Tue, 15 Jun 2021 23:18:52 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org
Cc:     benh@...nel.crashing.org, boqun.feng@...il.com, bp@...en8.de,
        catalin.marinas@....com, dvyukov@...gle.com, elver@...gle.com,
        ink@...assic.park.msu.ru, jonas@...thpole.se,
        juri.lelli@...hat.com, linux@...linux.org.uk, luto@...nel.org,
        mark.rutland@....com, mattst88@...il.com, mingo@...hat.com,
        monstr@...str.eu, paulmck@...nel.org, paulus@...ba.org,
        peterz@...radead.org, rth@...ddle.net, shorne@...il.com,
        stefan.kristiansson@...nalahti.fi, tglx@...utronix.de,
        vincent.guittot@...aro.org, will@...nel.org
Subject: Re: [RFC PATCH 09/10] powerpc: snapshot thread flags

Mark Rutland <mark.rutland@....com> writes:
> Some thread flags can be set remotely, and so even when IRQs are
> disabled, the flags can change under our feet. Generally this is
> unlikely to cause a problem in practice, but it is somewhat unsound, and
> KCSAN will legitimately warn that there is a data race.
>
> To avoid such issues, we should snapshot the flags prior to using them.
> Let's use the new helpers to do so on powerpc.
>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Paul Mackerras <paulus@...ba.org>
> ---
>  arch/powerpc/kernel/interrupt.c     | 16 ++++++++--------
>  arch/powerpc/kernel/ptrace/ptrace.c |  3 +--
>  2 files changed, 9 insertions(+), 10 deletions(-)

This looks good.

Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)


But, it clashes terribly with a series I'm planning to take for v5.14
that reworks our interrupt return code.

https://lore.kernel.org/linuxppc-dev/20210610130921.706938-1-npiggin@gmail.com/T/#t

So if you're also targeting v5.14 then it might be best to drop this
patch from the series, and we can do the conversion later.

cheers