From: Eric Dumazet <edumazet@xxxxxxxxxx>
v5.4.290-rt96-rc1 stable review patch.
If anyone has any objections, please let me know.
-----------
[ Upstream commit 316580b69d0a7aeeee5063af47438b626bc47cbd ]
On 64bit arches, struct u64_stats_sync is empty and provides
no help against load/store tearing.
Using READ_ONCE()/WRITE_ONCE() would be needed.
But the update side would be slightly more expensive.
local64_t was defined so that we could use regular adds
in a manner which is atomic wrt IRQs.
However the u64_stats infra means we do not have to use
local64_t on 32bit arches since the syncp provides the needed
protection.
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Tom Zanussi <zanussi@xxxxxxxxxx>
---
include/linux/u64_stats_sync.h | 51 +++++++++++++++++++++++++++++++---
1 file changed, 47 insertions(+), 4 deletions(-)
diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h
index ca40163933e33..a1f656fc317e6 100644
--- a/include/linux/u64_stats_sync.h
+++ b/include/linux/u64_stats_sync.h
@@ -40,8 +40,8 @@
* spin_lock_bh(...) or other synchronization to get exclusive access
* ...
* u64_stats_update_begin(&stats->syncp);
- * stats->bytes64 += len; // non atomic operation
- * stats->packets64++; // non atomic operation
+ * u64_stats_add(&stats->bytes64, len); // non atomic operation
+ * u64_stats_inc(&stats->packets64); // non atomic operation
* u64_stats_update_end(&stats->syncp);
*
* While a consumer (reader) should use following template to get consistent
@@ -52,8 +52,8 @@
*
* do {
* start = u64_stats_fetch_begin(&stats->syncp);
- * tbytes = stats->bytes64; // non atomic operation
- * tpackets = stats->packets64; // non atomic operation
+ * tbytes = u64_stats_read(&stats->bytes64); // non atomic operation
+ * tpackets = u64_stats_read(&stats->packets64); // non atomic operation
* } while (u64_stats_fetch_retry(&stats->syncp, start));
*
*
@@ -68,6 +68,49 @@ struct u64_stats_sync {
#endif
};
+#if BITS_PER_LONG == 64
+#include <asm/local64.h>
+
+typedef struct {
+ local64_t v;
+} u64_stats_t ;
+
+static inline u64 u64_stats_read(const u64_stats_t *p)
+{
+ return local64_read(&p->v);
+}
+
+static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
+{
+ local64_add(val, &p->v);
+}
+
+static inline void u64_stats_inc(u64_stats_t *p)
+{
+ local64_inc(&p->v);
+}
+
+#else
+
+typedef struct {
+ u64 v;
+} u64_stats_t;
+
+static inline u64 u64_stats_read(const u64_stats_t *p)
+{
+ return p->v;
+}
+
+static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
+{
+ p->v += val;
+}
+
+static inline void u64_stats_inc(u64_stats_t *p)
+{
+ p->v++;
+}
+#endif
#if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
#define u64_stats_init(syncp) \
--
2.43.0
