linux-kernel - Re: [PATCH 2/3] lib/Kconfig.debug: disable LOCK_DEBUGGING

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Date: Fri, 21 Jun 2024 18:02:26 +0300
From: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
To: Alexander Potapenko <glider@...gle.com>
Cc: elver@...gle.com, dvyukov@...gle.com, dave.hansen@...ux.intel.com, 
	peterz@...radead.org, akpm@...ux-foundation.org, x86@...nel.org, 
	linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH 2/3] lib/Kconfig.debug: disable LOCK_DEBUGGING_SUPPORT
 under KMSAN

On Fri, Jun 21, 2024 at 11:49:00AM +0200, Alexander Potapenko wrote:
> At least on x86 KMSAN is seriously slown down by lockdep, as every
> pfn_valid() call (which is done on every instrumented memory access
> in the kernel) performs several lockdep checks, all of which, in turn,
> perform additional memory accesses and call KMSAN instrumentation.
> 
> Right now lockdep overflows the stack under KMSAN, but even if we use
> reentrancy counters to avoid the recursion on the KMSAN side, the slowdown
> from lockdep remains big enough for the kernel to become unusable.
> 
> Reported-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Closes: https://github.com/google/kmsan/issues/94
> Link: https://groups.google.com/g/kasan-dev/c/ZBiGzZL36-I/m/WtNuKqP9EQAJ
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> ---
>  lib/Kconfig.debug | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 59b6765d86b8f..036905cf1dbe9 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1339,7 +1339,7 @@ menu "Lock Debugging (spinlocks, mutexes, etc...)"
>  
>  config LOCK_DEBUGGING_SUPPORT
>  	bool
> -	depends on TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
> +	depends on TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT && !KMSAN

Nit: no need to pile everything in one line. Add "depends on !KMSAN" on a
separate line.

Otherwise, looks sane.

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov