[PATCH net-next 1/4] u64_stats: Introduce u64_stats_copy()
From: David Yang <mmyangfl@gmail.com>
Date: 2026-01-20 09:22:47
Also in:
bridge, lkml
Subsystem:
the rest · Maintainer:
Linus Torvalds
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 <mmyangfl@gmail.com>
---
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..849ff6e159c6 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 <linux/string.h> 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;
--
2.51.0