From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Rohan McLure <rmclure@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Sasha Levin <sashal@kernel.org>, npiggin@gmail.com,
        christophe.leroy@csgroup.eu, ganeshgr@linux.ibm.com,
        alexandre.belloni@bootlin.com, heying24@huawei.com,
        linuxppc-dev@lists.ozlabs.org
Subject: [PATCH AUTOSEL 6.2 12/16] powerpc/kcsan: Exclude udelay to prevent recursive instrumentation
Date:   Sun,  5 Mar 2023 08:52:03 -0500
Message-Id: <20230305135207.1793266-12-sashal@kernel.org>
In-Reply-To: <20230305135207.1793266-1-sashal@kernel.org>
References: <20230305135207.1793266-1-sashal@kernel.org>
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From: Rohan McLure <rmclure@linux.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@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230206021801.105268-3-rmclure@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.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 e26eb6618ae5d..9d8665910350c 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -356,7 +356,7 @@ void vtime_flush(struct task_struct *tsk)
 }
 #endif /* CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
 
-void __delay(unsigned long loops)
+void __no_kcsan __delay(unsigned long loops)
 {
 	unsigned long start;
 
@@ -377,7 +377,7 @@ 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