[PATCH] locking/percpu-rwsem: Annotate intentional data race in readers_active_check()

[Sun Shaojie]

KCSAN reports a data race in readers_active_check():

  BUG: KCSAN: data-race in readers_active_check / percpu_down_write

  race at unknown origin, with read to 0xffff9f3eb5bf5f30 of 4 bytes
  by task 1271 on cpu 14:
   readers_active_check+0x...
   percpu_down_write+0x152/0x1f0

  value changed: 0xfffffff9 -> 0xfffffff8

This is a benign race. Annotate it with data_race() to suppress the
KCSAN warning.

Signed-off-by: Sun Shaojie <sunshaojie@xxxxxxxxxx>
---
 kernel/locking/percpu-rwsem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index f7e152c40d6d..6c78961fe753 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -211,7 +211,7 @@ EXPORT_SYMBOL_GPL(percpu_is_read_locked);
  */
 static bool readers_active_check(struct percpu_rw_semaphore *sem)
 {
-	if (per_cpu_sum(*sem->read_count) != 0)
+	if (data_race(per_cpu_sum(*sem->read_count)) != 0)
 		return false;
 
 	/*
-- 
2.25.1