From df153517e4d4403d13d603cccef68255783d396b Mon Sep 17 00:00:00 2001 From: David Yang Date: Tue, 20 Jan 2026 17:21:29 +0800 Subject: [PATCH] u64_stats: Introduce u64_stats_copy() The following (anti-)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, especially for memcpy(), for which arches may provide their highly-optimized implements. In theory the affected code should convert to u64_stats_t, or use READ_ONCE()/WRITE_ONCE() properly. However since there are needs to copy chunks of statistics, instead of writing loops at random places, we provide a safe memcpy() variant for u64_stats. Signed-off-by: David Yang Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260120092137.2161162-2-mmyangfl@gmail.com Signed-off-by: Jakub Kicinski --- 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 457879938fc19..849ff6e159c65 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_copy(void *dst, const void *src, size_t len) +{ + BUILD_BUG_ON(len % sizeof(u64_stats_t)); + for (size_t i = 0; i < len / sizeof(u64_stats_t); i++) + ((u64 *)dst)[i] = local64_read(&((local64_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_copy(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; -- 2.47.3