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>
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index b9e006a..651ca79 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -280,9 +280,7 @@
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 @@
{
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 @@
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;
diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index 892ae27..9e7328b 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -438,7 +438,7 @@
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))