===================================================================
@@ -451,19 +451,26 @@ static void dm_stat_for_entry(struct dm_
struct dm_stat_percpu *p;
/*
- * For strict correctness we should use local_irq_disable/enable
+ * For strict correctness we should use local_irq_save/restore
* instead of preempt_disable/enable.
*
- * This is racy if the driver finishes bios from non-interrupt
- * context as well as from interrupt context or from more different
- * interrupts.
+ * preempt_disable/enable is racy if the driver finishes bios
+ * from non-interrupt context as well as from interrupt context
+ * or from more different interrupts.
*
- * However, the race only results in not counting some events,
- * so it is acceptable.
+ * On 64-bit architectures the race only results in not counting some
+ * events, so it is acceptable. On 32-bit architectures the race could
+ * cause the counter going off by 2^32, so we need to do proper locking
+ * there.
*
* part_stat_lock()/part_stat_unlock() have this race too.
*/
+#if BITS_PER_LONG == 32
+ unsigned long flags;
+ local_irq_save(flags);
+#else
preempt_disable();
+#endif
p = &s->stat_percpu[smp_processor_id()][entry];
if (!end) {
@@ -478,7 +485,11 @@ static void dm_stat_for_entry(struct dm_
p->ticks[idx] += duration;
}
+#if BITS_PER_LONG == 32
+ local_irq_restore(flags);
+#else
preempt_enable();
+#endif
}
static void __dm_stat_bio(struct dm_stat *s, unsigned long bi_rw,
Hi I found this bug when reading through the statistics patch. That trick to avoid irq disabling can be done on 64-bit architectures, but not on 32-bit. Push this patch upstream. Mikulas --- dm-statistics: fix a possible counter corruption on 32-bit systems There was a deliberate race condition in dm_stat_for_entry to avoid the overhead disabling and enabling interrupts. The race could result in some events not being counted. However, on 32-bit architectures, operations on long long variables are not atomic, so the race condition could cause the counter to jump by 2^32. Such jumps could be disruptive, so we need to do proper locking on 32-bit architectures. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> --- drivers/md/dm-stats.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel