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From:   andrey.konovalov@linux.dev
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com,
        Catalin Marinas <catalin.marinas@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH 2/2] arm64: stacktrace: use non-atomic __set_bit
Date:   Sun, 22 May 2022 01:50:59 +0200
Message-Id: <a584e95f613d59c7ff45686c2805deb63bd61442.1653177005.git.andreyknvl@google.com>
In-Reply-To: <697e015e22ea78b021c2546f390ad5d773f3af86.1653177005.git.andreyknvl@google.com>
References: <697e015e22ea78b021c2546f390ad5d773f3af86.1653177005.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

Use the non-atomic version of set_bit() in arch/arm64/kernel/stacktrace.c,
as there is no concurrent accesses to frame->prev_type.

This speeds up stack trace collection and improves the boot time of
Generic KASAN by 2-5%.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/kernel/stacktrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 33e96ae4b15f..03593d451b0a 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -103,7 +103,7 @@ static int notrace unwind_frame(struct task_struct *tsk,
 		if (fp <= frame->prev_fp)
 			return -EINVAL;
 	} else {
-		set_bit(frame->prev_type, frame->stacks_done);
+		__set_bit(frame->prev_type, frame->stacks_done);
 	}
 
 	/*
-- 
2.25.1