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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 08-15-2012, 11:08 PM
Mikulas Patocka
 
Default dm-bufio & dm-verity: use ACCESS_ONCE instead of volatile

Hi

This is a simple cleanup patch.

Mikulas

---

dm-bufio & dm-verity: use ACCESS_ONCE instead of volatile

If the variable can be asynchronously modified and we want to prevent
compiler optimizations that could assume that the variable is the same,
use ACCESS_ONCE macro, as documented in Documentation/atomic_ops.txt.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
drivers/md/dm-bufio.c | 6 +++---
drivers/md/dm-verity.c | 2 +-
2 files changed, 4 insertions(+), 4 deletions(-)

Index: linux-3.5.1-fast/drivers/md/dm-bufio.c
================================================== =================
--- linux-3.5.1-fast.orig/drivers/md/dm-bufio.c 2012-08-16 00:46:43.000000000 +0200
+++ linux-3.5.1-fast/drivers/md/dm-bufio.c 2012-08-16 00:49:08.000000000 +0200
@@ -280,7 +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 = *(volatile unsigned long *)&dm_bufio_cache_size;
+ dm_bufio_cache_size_latch = ACCESS_ONCE(dm_bufio_cache_size);

/*
* Use default if set to 0 and report the actual cache size used.
@@ -811,7 +811,7 @@ static void __get_memory_limit(struct dm
{
unsigned long buffers;

- if (*(volatile unsigned long *)&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);
@@ -1589,7 +1589,7 @@ EXPORT_SYMBOL_GPL(dm_bufio_client_destro

static void cleanup_old_buffers(void)
{
- unsigned long max_age = *(volatile unsigned *)&dm_bufio_max_age;
+ unsigned long max_age = ACCESS_ONCE(dm_bufio_max_age);
struct dm_bufio_client *c;

if (max_age > ULONG_MAX / HZ)
Index: linux-3.5.1-fast/drivers/md/dm-verity.c
================================================== =================
--- linux-3.5.1-fast.orig/drivers/md/dm-verity.c 2012-08-16 00:46:14.000000000 +0200
+++ linux-3.5.1-fast/drivers/md/dm-verity.c 2012-08-16 00:47:11.000000000 +0200
@@ -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))

--
dm-devel mailing list
dm-devel@redhat.com
https://www.redhat.com/mailman/listinfo/dm-devel
 
Old 09-17-2012, 07:21 PM
Mikulas Patocka
 
Default dm-bufio & dm-verity: use ACCESS_ONCE instead of volatile

dm-bufio & dm-verity: use ACCESS_ONCE instead of volatile

If the variable can be asynchronously modified and we want to prevent
compiler optimizations that could assume that the variable is the same,
use ACCESS_ONCE macro, as documented in Documentation/atomic_ops.txt.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
drivers/md/dm-bufio.c | 10 +++-------
drivers/md/dm-verity.c | 2 +-
2 files changed, 4 insertions(+), 8 deletions(-)

---

Index: linux-3.5.3-fast/drivers/md/dm-bufio.c
================================================== =================
--- linux-3.5.3-fast.orig/drivers/md/dm-bufio.c 2012-09-17 21:13:18.000000000 +0200
+++ linux-3.5.3-fast/drivers/md/dm-bufio.c 2012-09-17 21:14:29.000000000 +0200
@@ -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.
@@ -813,7 +811,7 @@ 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);
@@ -1591,11 +1589,9 @@ 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-3.5.3-fast/drivers/md/dm-verity.c
================================================== =================
--- linux-3.5.3-fast.orig/drivers/md/dm-verity.c 2012-09-17 20:57:57.000000000 +0200
+++ linux-3.5.3-fast/drivers/md/dm-verity.c 2012-09-17 21:14:29.000000000 +0200
@@ -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))

--
dm-devel mailing list
dm-devel@redhat.com
https://www.redhat.com/mailman/listinfo/dm-devel
 

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