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>
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@ -280,9 +280,7 @@ static void __cache_size_refresh(void)
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BUG_ON(!mutex_is_locked(&dm_bufio_clients_lock));
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BUG_ON(!mutex_is_locked(&dm_bufio_clients_lock));
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BUG_ON(dm_bufio_client_count < 0);
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BUG_ON(dm_bufio_client_count < 0);
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dm_bufio_cache_size_latch = dm_bufio_cache_size;
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dm_bufio_cache_size_latch = ACCESS_ONCE(dm_bufio_cache_size);
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barrier();
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/*
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/*
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* Use default if set to 0 and report the actual cache size used.
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* Use default if set to 0 and report the actual cache size used.
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@ -812,7 +810,7 @@ static void __get_memory_limit(struct dm_bufio_client *c,
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{
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{
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unsigned long buffers;
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unsigned long buffers;
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if (dm_bufio_cache_size != dm_bufio_cache_size_latch) {
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if (ACCESS_ONCE(dm_bufio_cache_size) != dm_bufio_cache_size_latch) {
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mutex_lock(&dm_bufio_clients_lock);
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mutex_lock(&dm_bufio_clients_lock);
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__cache_size_refresh();
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__cache_size_refresh();
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mutex_unlock(&dm_bufio_clients_lock);
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mutex_unlock(&dm_bufio_clients_lock);
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@ -1590,11 +1588,9 @@ EXPORT_SYMBOL_GPL(dm_bufio_client_destroy);
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static void cleanup_old_buffers(void)
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static void cleanup_old_buffers(void)
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{
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{
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unsigned long max_age = dm_bufio_max_age;
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unsigned long max_age = ACCESS_ONCE(dm_bufio_max_age);
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struct dm_bufio_client *c;
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struct dm_bufio_client *c;
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barrier();
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if (max_age > ULONG_MAX / HZ)
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if (max_age > ULONG_MAX / HZ)
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max_age = ULONG_MAX / HZ;
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max_age = ULONG_MAX / HZ;
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@ -438,7 +438,7 @@ static void verity_prefetch_io(struct dm_verity *v, struct dm_verity_io *io)
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verity_hash_at_level(v, io->block, i, &hash_block_start, NULL);
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verity_hash_at_level(v, io->block, i, &hash_block_start, NULL);
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verity_hash_at_level(v, io->block + io->n_blocks - 1, i, &hash_block_end, NULL);
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verity_hash_at_level(v, io->block + io->n_blocks - 1, i, &hash_block_end, NULL);
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if (!i) {
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if (!i) {
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unsigned cluster = *(volatile unsigned *)&dm_verity_prefetch_cluster;
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unsigned cluster = ACCESS_ONCE(dm_verity_prefetch_cluster);
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cluster >>= v->data_dev_block_bits;
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cluster >>= v->data_dev_block_bits;
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if (unlikely(!cluster))
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if (unlikely(!cluster))
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