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dm: use ACCESS_ONCE for sysfs values

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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>
This commit is contained in:
Mikulas Patocka 2012-10-12 16:59:46 +01:00 committed by Alasdair G Kergon
parent 54499afbb8
commit fe5fe90639
2 changed files with 4 additions and 8 deletions
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10
drivers/md/dm-bufio.c
View File

@ -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;

2
drivers/md/dm-verity.c
View File

@ -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))