From 102a0743326a03cd1a1202ceda21e175b7d3575c Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Tue, 20 Feb 2024 01:20:52 +0000
Subject: [PATCH] add new system file
---
kernel/include/linux/u64_stats_sync.h | 94 +++++++++++++++++++++++++++++++++++------------
1 files changed, 70 insertions(+), 24 deletions(-)
diff --git a/kernel/include/linux/u64_stats_sync.h b/kernel/include/linux/u64_stats_sync.h
index 11096b5..e81856c 100644
--- a/kernel/include/linux/u64_stats_sync.h
+++ b/kernel/include/linux/u64_stats_sync.h
@@ -3,33 +3,36 @@
#define _LINUX_U64_STATS_SYNC_H
/*
- * To properly implement 64bits network statistics on 32bit and 64bit hosts,
- * we provide a synchronization point, that is a noop on 64bit or UP kernels.
+ * Protect against 64-bit values tearing on 32-bit architectures. This is
+ * typically used for statistics read/update in different subsystems.
*
* Key points :
- * 1) Use a seqcount on SMP 32bits, with low overhead.
- * 2) Whole thing is a noop on 64bit arches or UP kernels.
- * 3) Write side must ensure mutual exclusion or one seqcount update could
+ *
+ * - Use a seqcount on 32-bit SMP, only disable preemption for 32-bit UP.
+ * - The whole thing is a no-op on 64-bit architectures.
+ *
+ * Usage constraints:
+ *
+ * 1) Write side must ensure mutual exclusion, or one seqcount update could
* be lost, thus blocking readers forever.
- * If this synchronization point is not a mutex, but a spinlock or
- * spinlock_bh() or disable_bh() :
- * 3.1) Write side should not sleep.
- * 3.2) Write side should not allow preemption.
- * 3.3) If applicable, interrupts should be disabled.
+ *
+ * 2) Write side must disable preemption, or a seqcount reader can preempt the
+ * writer and also spin forever.
+ *
+ * 3) Write side must use the _irqsave() variant if other writers, or a reader,
+ * can be invoked from an IRQ context.
*
* 4) If reader fetches several counters, there is no guarantee the whole values
- * are consistent (remember point 1) : this is a noop on 64bit arches anyway)
+ * are consistent w.r.t. each other (remember point #2: seqcounts are not
+ * used for 64bit architectures).
*
- * 5) readers are allowed to sleep or be preempted/interrupted : They perform
- * pure reads. But if they have to fetch many values, it's better to not allow
- * preemptions/interruptions to avoid many retries.
+ * 5) Readers are allowed to sleep or be preempted/interrupted: they perform
+ * pure reads.
*
- * 6) If counter might be written by an interrupt, readers should block interrupts.
- * (On UP, there is no seqcount_t protection, a reader allowing interrupts could
- * read partial values)
- *
- * 7) For irq and softirq uses, readers can use u64_stats_fetch_begin_irq() and
- * u64_stats_fetch_retry_irq() helpers
+ * 6) Readers must use both u64_stats_fetch_{begin,retry}_irq() if the stats
+ * might be updated from a hardirq or softirq context (remember point #1:
+ * seqcounts are not used for UP kernels). 32-bit UP stat readers could read
+ * corrupted 64-bit values otherwise.
*
* Usage :
*
@@ -40,8 +43,8 @@
* 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 +55,8 @@
*
* 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 +71,49 @@
#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) seqcount_init(&(syncp)->seq)
--
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