Commit 5b25f70f authored by Arne Jansen's avatar Arne Jansen Committed by Jan Schmidt

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: default avatarArne Jansen <sensille@gmx.net>
Signed-off-by: default avatarJan Schmidt <list.btrfs@jan-o-sch.net>
parent eebe063b
...@@ -3571,6 +3571,7 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree, ...@@ -3571,6 +3571,7 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
atomic_set(&eb->blocking_writers, 0); atomic_set(&eb->blocking_writers, 0);
atomic_set(&eb->spinning_readers, 0); atomic_set(&eb->spinning_readers, 0);
atomic_set(&eb->spinning_writers, 0); atomic_set(&eb->spinning_writers, 0);
eb->lock_nested = 0;
init_waitqueue_head(&eb->write_lock_wq); init_waitqueue_head(&eb->write_lock_wq);
init_waitqueue_head(&eb->read_lock_wq); init_waitqueue_head(&eb->read_lock_wq);
......
...@@ -129,6 +129,7 @@ struct extent_buffer { ...@@ -129,6 +129,7 @@ struct extent_buffer {
struct list_head leak_list; struct list_head leak_list;
struct rcu_head rcu_head; struct rcu_head rcu_head;
atomic_t refs; atomic_t refs;
pid_t lock_owner;
/* count of read lock holders on the extent buffer */ /* count of read lock holders on the extent buffer */
atomic_t write_locks; atomic_t write_locks;
...@@ -137,6 +138,7 @@ struct extent_buffer { ...@@ -137,6 +138,7 @@ struct extent_buffer {
atomic_t blocking_readers; atomic_t blocking_readers;
atomic_t spinning_readers; atomic_t spinning_readers;
atomic_t spinning_writers; atomic_t spinning_writers;
int lock_nested;
/* protects write locks */ /* protects write locks */
rwlock_t lock; rwlock_t lock;
......
...@@ -33,6 +33,14 @@ void btrfs_assert_tree_read_locked(struct extent_buffer *eb); ...@@ -33,6 +33,14 @@ void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
*/ */
void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw) 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 (rw == BTRFS_WRITE_LOCK) {
if (atomic_read(&eb->blocking_writers) == 0) { if (atomic_read(&eb->blocking_writers) == 0) {
WARN_ON(atomic_read(&eb->spinning_writers) != 1); WARN_ON(atomic_read(&eb->spinning_writers) != 1);
...@@ -57,6 +65,14 @@ void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw) ...@@ -57,6 +65,14 @@ void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
*/ */
void btrfs_clear_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);
}
if (rw == BTRFS_WRITE_LOCK_BLOCKING) { if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
BUG_ON(atomic_read(&eb->blocking_writers) != 1); BUG_ON(atomic_read(&eb->blocking_writers) != 1);
write_lock(&eb->lock); write_lock(&eb->lock);
...@@ -81,12 +97,25 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw) ...@@ -81,12 +97,25 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
void btrfs_tree_read_lock(struct extent_buffer *eb) void btrfs_tree_read_lock(struct extent_buffer *eb)
{ {
again: 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); wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
read_lock(&eb->lock); read_lock(&eb->lock);
if (atomic_read(&eb->blocking_writers)) { if (atomic_read(&eb->blocking_writers)) {
read_unlock(&eb->lock); read_unlock(&eb->lock);
wait_event(eb->write_lock_wq,
atomic_read(&eb->blocking_writers) == 0);
goto again; goto again;
} }
atomic_inc(&eb->read_locks); atomic_inc(&eb->read_locks);
...@@ -129,6 +158,7 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb) ...@@ -129,6 +158,7 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb)
} }
atomic_inc(&eb->write_locks); atomic_inc(&eb->write_locks);
atomic_inc(&eb->spinning_writers); atomic_inc(&eb->spinning_writers);
eb->lock_owner = current->pid;
return 1; return 1;
} }
...@@ -137,6 +167,15 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb) ...@@ -137,6 +167,15 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb)
*/ */
void btrfs_tree_read_unlock(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);
}
btrfs_assert_tree_read_locked(eb); btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->spinning_readers) == 0); WARN_ON(atomic_read(&eb->spinning_readers) == 0);
atomic_dec(&eb->spinning_readers); atomic_dec(&eb->spinning_readers);
...@@ -149,6 +188,15 @@ void btrfs_tree_read_unlock(struct extent_buffer *eb) ...@@ -149,6 +188,15 @@ void btrfs_tree_read_unlock(struct extent_buffer *eb)
*/ */
void btrfs_tree_read_unlock_blocking(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);
}
btrfs_assert_tree_read_locked(eb); btrfs_assert_tree_read_locked(eb);
WARN_ON(atomic_read(&eb->blocking_readers) == 0); WARN_ON(atomic_read(&eb->blocking_readers) == 0);
if (atomic_dec_and_test(&eb->blocking_readers)) if (atomic_dec_and_test(&eb->blocking_readers))
...@@ -181,6 +229,7 @@ int btrfs_tree_lock(struct extent_buffer *eb) ...@@ -181,6 +229,7 @@ int btrfs_tree_lock(struct extent_buffer *eb)
WARN_ON(atomic_read(&eb->spinning_writers)); WARN_ON(atomic_read(&eb->spinning_writers));
atomic_inc(&eb->spinning_writers); atomic_inc(&eb->spinning_writers);
atomic_inc(&eb->write_locks); atomic_inc(&eb->write_locks);
eb->lock_owner = current->pid;
return 0; return 0;
} }
......
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