linux-kernel - [PATCH] powerpc/kcsan: Properly instrument arch_spin

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Date:   Fri, 26 May 2023 07:57:33 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Marco Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev@...glegroups.com, Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/kcsan: Properly instrument arch_spin_unlock()

The following boottime error is encountered with SMP kernel:

  kcsan: improperly instrumented type=(0): arch_spin_unlock(&arch_spinlock)
  kcsan: improperly instrumented type=(0): spin_unlock(&test_spinlock)
  kcsan: improperly instrumented type=(KCSAN_ACCESS_WRITE): arch_spin_unlock(&arch_spinlock)
  kcsan: improperly instrumented type=(KCSAN_ACCESS_WRITE): spin_unlock(&test_spinlock)
  kcsan: improperly instrumented type=(KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND): arch_spin_unlock(&arch_spinlock)
  kcsan: improperly instrumented type=(KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND): spin_unlock(&test_spinlock)
  kcsan: selftest: test_barrier failed
  kcsan: selftest: 2/3 tests passed
  Kernel panic - not syncing: selftests failed

Properly instrument arch_spin_unlock() with kcsan_mb().

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/include/asm/simple_spinlock.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/include/asm/simple_spinlock.h b/arch/powerpc/include/asm/simple_spinlock.h
index 9dcc7e9993b9..4dd12dcb9ef8 100644
--- a/arch/powerpc/include/asm/simple_spinlock.h
+++ b/arch/powerpc/include/asm/simple_spinlock.h
@@ -15,6 +15,7 @@
  * (the type definitions are in asm/simple_spinlock_types.h)
  */
 #include <linux/irqflags.h>
+#include <linux/kcsan-checks.h>
 #include <asm/paravirt.h>
 #include <asm/paca.h>
 #include <asm/synch.h>
@@ -126,6 +127,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
 
 static inline void arch_spin_unlock(arch_spinlock_t *lock)
 {
+	kcsan_mb();
 	__asm__ __volatile__("# arch_spin_unlock\n\t"
 				PPC_RELEASE_BARRIER: : :"memory");
 	lock->slock = 0;
-- 
2.40.1