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 (file)
--- 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;
 

diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index 892ae27..9e7328b 100644 (file)
--- 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))