linux-kernel - Re: [RFC PATCH 08/10] openrisc: snapshot thread flags

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Date:   Fri, 11 Jun 2021 04:14:45 +0900
From:   Stafford Horne <shorne@...il.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, 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, mattst88@...il.com, mingo@...hat.com,
        monstr@...str.eu, mpe@...erman.id.au, paulmck@...nel.org,
        paulus@...ba.org, peterz@...radead.org, rth@...ddle.net,
        stefan.kristiansson@...nalahti.fi, tglx@...utronix.de,
        vincent.guittot@...aro.org, will@...nel.org
Subject: Re: [RFC PATCH 08/10] openrisc: snapshot thread flags

On Wed, Jun 09, 2021 at 01:19:59PM +0100, Mark Rutland wrote:
> 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 openrisc.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Jonas Bonn <jonas@...thpole.se>
> Cc: Stafford Horne <shorne@...il.com>
> Cc: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
> ---
>  arch/openrisc/kernel/signal.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/openrisc/kernel/signal.c b/arch/openrisc/kernel/signal.c
> index 1ebcff271096..a730a914c2b4 100644
> --- a/arch/openrisc/kernel/signal.c
> +++ b/arch/openrisc/kernel/signal.c
> @@ -315,7 +315,7 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
>  			}
>  		}
>  		local_irq_disable();
> -		thread_flags = current_thread_info()->flags;
> +		thread_flags = read_thread_flags();
>  	} while (thread_flags & _TIF_WORK_MASK);
>  	return 0;
>  }

This looks good to me.  As per patch 01/10 this adds a READ_ONCE around the
original flags read.

Acked-by: Stafford Horne <shorne@...il.com>