Commit df153517 authored Jan 20, 2026 by David Yang Committed by Jakub Kicinski Jan 25, 2026

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 <mmyangfl@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260120092137.2161162-2-mmyangfl@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

parent 3085ff59

include/linux/u64_stats_sync.h

+15 −0

Original line number	Diff line number	Diff line
		@@ -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;