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, 1 insertions, 1 deletions

diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index 892ae2766aa6..9e7328bb4030 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -438,7 +438,7 @@ static void verity_prefetch_io(struct dm_verity *v, struct dm_verity_io *io)
                 verity_hash_at_level(v, io->block, i, &hash_block_start, NULL);
                 verity_hash_at_level(v, io->block + io->n_blocks - 1, i, &hash_block_end, NULL);
                 if (!i) {
-                        unsigned cluster = *(volatile unsigned *)&dm_verity_prefetch_cluster;
+                        unsigned cluster = ACCESS_ONCE(dm_verity_prefetch_cluster);
 
                         cluster >>= v->data_dev_block_bits;
                         if (unlikely(!cluster))