Re: [PATCH 4/5] kmsan: make sure PREEMPT_RT is off

Peter Zijlstra
2022-11-02T12:53:08Z

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
>