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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Nikolay Aleksandrov , Ido Schimmel , Simon Horman , Aaron Conole , Eelco Chaudron , Ilya Maximets , Shigeru Yoshida , Stanislav Fomichev , Breno Leitao , Carolina Jubran , Kuniyuki Iwashima , Guillaume Nault , linux-kernel@vger.kernel.org, bridge@lists.linux.dev, dev@openvswitch.org Subject: [PATCH net-next v2 1/7] u64_stats: Introduce u64_stats_reads() Date: Sat, 24 Jan 2026 00:21:33 +0800 Message-ID: <20260123162159.2877941-2-mmyangfl@gmail.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260123162159.2877941-1-mmyangfl@gmail.com> References: <20260123162159.2877941-1-mmyangfl@gmail.com> Precedence: bulk X-Mailing-List: bridge@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The following pattern was observed in the code tree: do { start = u64_stats_fetch_begin(&pstats->syncp); memcpy(&temp, &pstats->stats, sizeof(temp)); } while (u64_stats_fetch_retry(&pstats->syncp, start)); On 64bit arches, struct u64_stats_sync is empty and provides no help against load/store tearing. memcpy() or struct copying does not guarantee tear free, although compilers never generate such instructions in practice. Theoretically the affected code should convert to u64_stats_t, or use atomic operations properly. However since there are needs to copy chunks of statistics, instead of writing loops everywhere, we provide a safe memcpy() variant for that purpose. Signed-off-by: David Yang --- include/linux/u64_stats_sync.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h index 457879938fc1..15ea4db2a77b 100644 --- a/include/linux/u64_stats_sync.h +++ b/include/linux/u64_stats_sync.h @@ -79,6 +79,14 @@ static inline u64 u64_stats_read(const u64_stats_t *p) return local64_read(&p->v); } +static inline void *u64_stats_reads(void *dst, const void *src, size_t len) +{ + BUILD_BUG_ON(len % sizeof(u64_stats_t)); + for (size_t i = 0; i < len; i += sizeof(u64_stats_t)) + *(u64 *)(dst + i) = u64_stats_read((const u64_stats_t *)(src + i)); + return dst; +} + static inline void u64_stats_set(u64_stats_t *p, u64 val) { local64_set(&p->v, val); @@ -110,6 +118,7 @@ static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp, } #else /* 64 bit */ +#include typedef struct { u64 v; @@ -120,6 +129,12 @@ static inline u64 u64_stats_read(const u64_stats_t *p) return p->v; } +static inline void *u64_stats_reads(void *dst, const void *src, size_t len) +{ + BUILD_BUG_ON(len % sizeof(u64_stats_t)); + return memcpy(dst, src, len); +} + static inline void u64_stats_set(u64_stats_t *p, u64 val) { p->v = val; -- 2.51.0