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Peter Anvin" , Peter Zijlstra Subject: [PATCH v2 2/4] locking/atomic/x86: Introduce arch_atomic64_read_tearable to x86_32 Date: Tue, 9 Apr 2024 18:30:30 +0200 Message-ID: <20240409163200.188498-2-ubizjak@gmail.com> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20240409163200.188498-1-ubizjak@gmail.com> References: <20240409163200.188498-1-ubizjak@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Introduce arch_atomic64_read_tearable for 32-bit targets to load the value from atomic64_t location in a non-atomic way. The read might be torn, but can safely be consumed by the 64-bit compare-and-swap loop. Signed-off-by: Uros Bizjak Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: Peter Zijlstra --- arch/x86/include/asm/atomic64_32.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/arch/x86/include/asm/atomic64_32.h b/arch/x86/include/asm/atomic64_32.h index 11e817dab44a..b4434e5ae31d 100644 --- a/arch/x86/include/asm/atomic64_32.h +++ b/arch/x86/include/asm/atomic64_32.h @@ -14,6 +14,20 @@ typedef struct { #define ATOMIC64_INIT(val) { (val) } +/* + * This function is intended to load the value from atomic64_t + * location in a non-atomic way. The read might be torn, but can + * safely be consumed by the 64-bit compare-and-swap loop. + */ +static __always_inline s64 arch_atomic64_read_tearable(const atomic64_t *v) +{ + /* + * See the comment in arch_atomic_read() on why we use + * __READ_ONCE() instead of READ_ONCE_NOCHECK() here. + */ + return __READ_ONCE(v->counter); +} + #define __ATOMIC64_DECL(sym) void atomic64_##sym(atomic64_t *, ...) #ifndef ATOMIC64_EXPORT #define ATOMIC64_DECL_ONE __ATOMIC64_DECL -- 2.42.0