linux-kernel - [PATCH AUTOSEL 5.15 5/9] powerpc/kcsan: Exclude udelay to prevent recursive instrumentation

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Date:   Sun,  5 Mar 2023 08:53:55 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Rohan McLure <rmclure@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>, npiggin@...il.com,
        christophe.leroy@...roup.eu, alexandre.belloni@...tlin.com,
        heying24@...wei.com, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 5.15 5/9] powerpc/kcsan: Exclude udelay to prevent recursive instrumentation

From: Rohan McLure <rmclure@...ux.ibm.com>

[ Upstream commit 2a7ce82dc46c591c9244057d89a6591c9639b9b9 ]

In order for KCSAN to increase its likelihood of observing a data race,
it sets a watchpoint on memory accesses and stalls, allowing for
detection of conflicting accesses by other kernel threads or interrupts.

Stalls are implemented by injecting a call to udelay in instrumented code.
To prevent recursive instrumentation, exclude udelay from being instrumented.

Signed-off-by: Rohan McLure <rmclure@...ux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20230206021801.105268-3-rmclure@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/kernel/time.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 934d8ae66cc63..4406d7a89558b 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -450,7 +450,7 @@ void vtime_flush(struct task_struct *tsk)
 #define calc_cputime_factors()
 #endif
 
-void __delay(unsigned long loops)
+void __no_kcsan __delay(unsigned long loops)
 {
 	unsigned long start;
 
@@ -471,7 +471,7 @@ void __delay(unsigned long loops)
 }
 EXPORT_SYMBOL(__delay);
 
-void udelay(unsigned long usecs)
+void __no_kcsan udelay(unsigned long usecs)
 {
 	__delay(tb_ticks_per_usec * usecs);
 }
-- 
2.39.2