dm: use ACCESS_ONCE for sysfs values

Use the ACCESS_ONCE macro in dm-bufio and dm-verity where a variable
can be modified asynchronously (through sysfs) and we want to prevent
compiler optimizations that assume that the variable hasn't changed.
(See Documentation/atomic_ops.txt.)

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 3 insertions, 7 deletions

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index b9e006aa6062..651ca79881dd 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -280,9 +280,7 @@ static void __cache_size_refresh(void)
         BUG_ON(!mutex_is_locked(&dm_bufio_clients_lock));
         BUG_ON(dm_bufio_client_count < 0);
 
-        dm_bufio_cache_size_latch = dm_bufio_cache_size;
-
-        barrier();
+        dm_bufio_cache_size_latch = ACCESS_ONCE(dm_bufio_cache_size);
 
         /*
          * Use default if set to 0 and report the actual cache size used.
@@ -812,7 +810,7 @@ static void __get_memory_limit(struct dm_bufio_client *c,
 {
         unsigned long buffers;
 
-        if (dm_bufio_cache_size != dm_bufio_cache_size_latch) {
+        if (ACCESS_ONCE(dm_bufio_cache_size) != dm_bufio_cache_size_latch) {
                 mutex_lock(&dm_bufio_clients_lock);
                 __cache_size_refresh();
                 mutex_unlock(&dm_bufio_clients_lock);
@@ -1590,11 +1588,9 @@ EXPORT_SYMBOL_GPL(dm_bufio_client_destroy);
 
 static void cleanup_old_buffers(void)
 {
-        unsigned long max_age = dm_bufio_max_age;
+        unsigned long max_age = ACCESS_ONCE(dm_bufio_max_age);
         struct dm_bufio_client *c;
 
-        barrier();
-
         if (max_age > ULONG_MAX / HZ)
                 max_age = ULONG_MAX / HZ;