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

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Message-ID: <20240621094901.1360454-2-glider@google.com>
Date: Fri, 21 Jun 2024 11:49:00 +0200
From: Alexander Potapenko <glider@...gle.com>
To: 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, 
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH 2/3] lib/Kconfig.debug: disable LOCK_DEBUGGING_SUPPORT under KMSAN

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
 	default y
 
 config PROVE_LOCKING
-- 
2.45.2.741.gdbec12cfda-goog