Btrfs: add nested locking mode for paths
This patch adds the possibilty to read-lock an extent even if it is already
write-locked from the same thread. btrfs_find_all_roots() needs this
capability.
Signed-off-by: Arne Jansen <sensille@gmx.net>
Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index d77b67c..5e178d8 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -33,6 +33,14 @@
*/
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);
+ }
if (rw == BTRFS_WRITE_LOCK) {
if (atomic_read(&eb->blocking_writers) == 0) {
WARN_ON(atomic_read(&eb->spinning_writers) != 1);
@@ -57,6 +65,14 @@
*/
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);
+ }
if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
BUG_ON(atomic_read(&eb->blocking_writers) != 1);
write_lock(&eb->lock);
@@ -81,12 +97,25 @@
void btrfs_tree_read_lock(struct extent_buffer *eb)
{
again:
+ read_lock(&eb->lock);
+ if (atomic_read(&eb->blocking_writers) &&
+ current->pid == eb->lock_owner) {
+ /*
+ * This extent is already write-locked by our thread. We allow
+ * an additional read lock to be added because it's for the same
+ * thread. btrfs_find_all_roots() depends on this as it may be
+ * called on a partly (write-)locked tree.
+ */
+ BUG_ON(eb->lock_nested);
+ eb->lock_nested = 1;
+ read_unlock(&eb->lock);
+ return;
+ }
+ read_unlock(&eb->lock);
wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
read_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers)) {
read_unlock(&eb->lock);
- wait_event(eb->write_lock_wq,
- atomic_read(&eb->blocking_writers) == 0);
goto again;
}
atomic_inc(&eb->read_locks);
@@ -129,6 +158,7 @@
}
atomic_inc(&eb->write_locks);
atomic_inc(&eb->spinning_writers);
+ eb->lock_owner = current->pid;
return 1;
}
@@ -137,6 +167,15 @@
*/
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);
+ }
btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->spinning_readers) == 0);
atomic_dec(&eb->spinning_readers);
@@ -149,6 +188,15 @@
*/
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);
+ }
btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->blocking_readers) == 0);
if (atomic_dec_and_test(&eb->blocking_readers))
@@ -181,6 +229,7 @@
WARN_ON(atomic_read(&eb->spinning_writers));
atomic_inc(&eb->spinning_writers);
atomic_inc(&eb->write_locks);
+ eb->lock_owner = current->pid;
return 0;
}