From: Ye Bin <yebin10@xxxxxxxxxx>
In commit 8b57b11cca88 ("pcpcntrs: fix dying cpu summation race") a race
condition between a cpu dying and percpu_counter_sum() iterating online CPUs
was identified.
Acctually, there's the same race condition between a cpu dying and
__percpu_counter_compare(). Here, use 'num_online_cpus()' for quick judgment.
But 'num_online_cpus()' will be decreased before call 'percpu_counter_cpu_dead()',
then maybe return incorrect result.
To solve above issue, also need to add dying CPUs count when do quick judgment
in __percpu_counter_compare().
Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
---
lib/percpu_counter.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 5004463c4f9f..399840cb0012 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -227,6 +227,15 @@ static int percpu_counter_cpu_dead(unsigned int cpu)
return 0;
}
+static __always_inline unsigned int num_count_cpus(void)
+{
+#ifdef CONFIG_HOTPLUG_CPU
+ return (num_online_cpus() + num_dying_cpus());
+#else
+ return num_online_cpus();
+#endif
+}
+
/*
* Compare counter against given value.
* Return 1 if greater, 0 if equal and -1 if less
@@ -237,7 +246,7 @@ int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
count = percpu_counter_read(fbc);
/* Check to see if rough count will be sufficient for comparison */
- if (abs(count - rhs) > (batch * num_online_cpus())) {
+ if (abs(count - rhs) > (batch * num_count_cpus())) {
if (count > rhs)
return 1;
else
--
2.31.1
