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-rw-r--r--fs/btrfs/locking.c80
1 files changed, 46 insertions, 34 deletions
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 01277b8f2373..5665d2149249 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -33,14 +33,14 @@ static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
*/
void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
{
- if (eb->lock_nested) {
- read_lock(&eb->lock);
- if (eb->lock_nested && current->pid == eb->lock_owner) {
- read_unlock(&eb->lock);
- return;
- }
- read_unlock(&eb->lock);
- }
+ /*
+ * no lock is required. The lock owner may change if
+ * we have a read lock, but it won't change to or away
+ * from us. If we have the write lock, we are the owner
+ * and it'll never change.
+ */
+ if (eb->lock_nested && current->pid == eb->lock_owner)
+ return;
if (rw == BTRFS_WRITE_LOCK) {
if (atomic_read(&eb->blocking_writers) == 0) {
WARN_ON(atomic_read(&eb->spinning_writers) != 1);
@@ -65,14 +65,15 @@ void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
*/
void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
{
- if (eb->lock_nested) {
- read_lock(&eb->lock);
- if (eb->lock_nested && current->pid == eb->lock_owner) {
- read_unlock(&eb->lock);
- return;
- }
- read_unlock(&eb->lock);
- }
+ /*
+ * no lock is required. The lock owner may change if
+ * we have a read lock, but it won't change to or away
+ * from us. If we have the write lock, we are the owner
+ * and it'll never change.
+ */
+ if (eb->lock_nested && current->pid == eb->lock_owner)
+ return;
+
if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
BUG_ON(atomic_read(&eb->blocking_writers) != 1);
write_lock(&eb->lock);
@@ -99,6 +100,9 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
void btrfs_tree_read_lock(struct extent_buffer *eb)
{
again:
+ BUG_ON(!atomic_read(&eb->blocking_writers) &&
+ current->pid == eb->lock_owner);
+
read_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers) &&
current->pid == eb->lock_owner) {
@@ -132,7 +136,9 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb)
if (atomic_read(&eb->blocking_writers))
return 0;
- read_lock(&eb->lock);
+ if (!read_trylock(&eb->lock))
+ return 0;
+
if (atomic_read(&eb->blocking_writers)) {
read_unlock(&eb->lock);
return 0;
@@ -151,7 +157,10 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb)
if (atomic_read(&eb->blocking_writers) ||
atomic_read(&eb->blocking_readers))
return 0;
- write_lock(&eb->lock);
+
+ if (!write_trylock(&eb->lock))
+ return 0;
+
if (atomic_read(&eb->blocking_writers) ||
atomic_read(&eb->blocking_readers)) {
write_unlock(&eb->lock);
@@ -168,14 +177,15 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb)
*/
void btrfs_tree_read_unlock(struct extent_buffer *eb)
{
- if (eb->lock_nested) {
- read_lock(&eb->lock);
- if (eb->lock_nested && current->pid == eb->lock_owner) {
- eb->lock_nested = 0;
- read_unlock(&eb->lock);
- return;
- }
- read_unlock(&eb->lock);
+ /*
+ * if we're nested, we have the write lock. No new locking
+ * is needed as long as we are the lock owner.
+ * The write unlock will do a barrier for us, and the lock_nested
+ * field only matters to the lock owner.
+ */
+ if (eb->lock_nested && current->pid == eb->lock_owner) {
+ eb->lock_nested = 0;
+ return;
}
btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->spinning_readers) == 0);
@@ -189,14 +199,15 @@ void btrfs_tree_read_unlock(struct extent_buffer *eb)
*/
void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
{
- if (eb->lock_nested) {
- read_lock(&eb->lock);
- if (eb->lock_nested && current->pid == eb->lock_owner) {
- eb->lock_nested = 0;
- read_unlock(&eb->lock);
- return;
- }
- read_unlock(&eb->lock);
+ /*
+ * if we're nested, we have the write lock. No new locking
+ * is needed as long as we are the lock owner.
+ * The write unlock will do a barrier for us, and the lock_nested
+ * field only matters to the lock owner.
+ */
+ if (eb->lock_nested && current->pid == eb->lock_owner) {
+ eb->lock_nested = 0;
+ return;
}
btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->blocking_readers) == 0);
@@ -244,6 +255,7 @@ void btrfs_tree_unlock(struct extent_buffer *eb)
BUG_ON(blockers > 1);
btrfs_assert_tree_locked(eb);
+ eb->lock_owner = 0;
atomic_dec(&eb->write_locks);
if (blockers) {