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Date:   Wed, 2 Nov 2022 13:53:00 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexander Potapenko <glider@google.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Marco Elver <elver@google.com>
Subject: Re: [PATCH 4/5] kmsan: make sure PREEMPT_RT is off
Message-ID: <Y2JoLOXtvmcVx8mU@hirez.programming.kicks-ass.net>
References: <20221102110611.1085175-1-glider@google.com>
 <20221102110611.1085175-4-glider@google.com>
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On Wed, Nov 02, 2022 at 12:06:10PM +0100, Alexander Potapenko wrote:
> As pointed out by Peter Zijlstra, __msan_poison_alloca() does not play
> well with IRQ code when PREEMPT_RT is on, because in that mode even
> GFP_ATOMIC allocations cannot be performed.
> 
> Fixing this would require making stackdepot completely lockless, which
> is quite challenging and may be excessive for the time being.
> 
> Instead, make sure KMSAN is incompatible with PREEMPT_RT, like other
> debug configs are.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Marco Elver <elver@google.com>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Link: https://lore.kernel.org/lkml/20221025221755.3810809-1-glider@google.com/
> Signed-off-by: Alexander Potapenko <glider@google.com>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> ---
>  lib/Kconfig.kmsan | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> index b2489dd6503fa..ef2c8f256c57d 100644
> --- a/lib/Kconfig.kmsan
> +++ b/lib/Kconfig.kmsan
> @@ -12,6 +12,7 @@ config KMSAN
>  	bool "KMSAN: detector of uninitialized values use"
>  	depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
>  	depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
> +	depends on !PREEMPT_RT
>  	select STACKDEPOT
>  	select STACKDEPOT_ALWAYS_INIT
>  	help
> -- 
> 2.38.1.273.g43a17bfeac-goog
>