From: Mikulas Patocka 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 Signed-off-by: Alasdair G Kergon --- drivers/md/dm-bufio.c | 10 +++------- drivers/md/dm-verity.c | 2 +- 2 files changed, 4 insertions(+), 8 deletions(-) Index: linux/drivers/md/dm-bufio.c =================================================================== --- linux.orig/drivers/md/dm-bufio.c +++ linux/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 { 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_destro 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; Index: linux/drivers/md/dm-verity.c =================================================================== --- linux.orig/drivers/md/dm-verity.c +++ linux/drivers/md/dm-verity.c @@ -438,7 +438,7 @@ static void verity_prefetch_io(struct dm 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))