linux-kernel - Re: [PATCH v2 4/8] mm/debug: Provide VM_WARN_ON_IRQS

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Date:   Thu, 1 Sep 2022 16:41:59 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Subject: Re: [PATCH v2 4/8] mm/debug: Provide VM_WARN_ON_IRQS_ENABLED()

On Thu 25-08-22 18:41:27, Sebastian Andrzej Siewior wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Some places in the VM code expect interrupts disabled, which is a valid
> expectation on non-PREEMPT_RT kernels, but does not hold on RT kernels in
> some places because the RT spinlock substitution does not disable
> interrupts.
> 
> To avoid sprinkling CONFIG_PREEMPT_RT conditionals into those places,
> provide VM_WARN_ON_IRQS_ENABLED() which is only enabled when VM_DEBUG=y and
> PREEMPT_RT=n.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-mm@...ck.org
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Acked-by: Michal Hocko <mhocko@...e.com>
Thanks!

> ---
>  include/linux/mmdebug.h | 6 ++++++
>  lib/Kconfig.debug       | 3 +++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index 15ae78cd28536..b8728d11c9490 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -94,6 +94,12 @@ void dump_mm(const struct mm_struct *mm);
>  #define VM_WARN(cond, format...) BUILD_BUG_ON_INVALID(cond)
>  #endif
>  
> +#ifdef CONFIG_DEBUG_VM_IRQSOFF
> +#define VM_WARN_ON_IRQS_ENABLED() WARN_ON_ONCE(!irqs_disabled())
> +#else
> +#define VM_WARN_ON_IRQS_ENABLED() do { } while (0)
> +#endif
> +
>  #ifdef CONFIG_DEBUG_VIRTUAL
>  #define VIRTUAL_BUG_ON(cond) BUG_ON(cond)
>  #else
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 072e4b289c13e..c96fc6820544c 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -803,6 +803,9 @@ config ARCH_HAS_DEBUG_VM_PGTABLE
>  	  An architecture should select this when it can successfully
>  	  build and run DEBUG_VM_PGTABLE.
>  
> +config DEBUG_VM_IRQSOFF
> +	def_bool DEBUG_VM && !PREEMPT_RT
> +
>  config DEBUG_VM
>  	bool "Debug VM"
>  	depends on DEBUG_KERNEL
> -- 
> 2.37.2

-- 
Michal Hocko
SUSE Labs