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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>
This commit is contained in:
Arne Jansen 2011-09-13 10:55:48 +02:00 committed by Jan Schmidt
parent eebe063b7f
commit 5b25f70f42
3 changed files with 54 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
fs/btrfs/extent_io.c
View File

@ -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->spinning_readers, 0);
atomic_set(&eb->spinning_writers, 0);
eb->lock_nested = 0;
init_waitqueue_head(&eb->write_lock_wq);
init_waitqueue_head(&eb->read_lock_wq);

2
fs/btrfs/extent_io.h
View File

@ -129,6 +129,7 @@ struct extent_buffer {
struct list_head leak_list;
struct rcu_head rcu_head;
atomic_t refs;
pid_t lock_owner;
/* count of read lock holders on the extent buffer */
atomic_t write_locks;
@ -137,6 +138,7 @@ struct extent_buffer {
atomic_t blocking_readers;
atomic_t spinning_readers;
atomic_t spinning_writers;
int lock_nested;
/* protects write locks */
rwlock_t lock;

53
fs/btrfs/locking.c
View File

@ -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)
{
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_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);
}
if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
BUG_ON(atomic_read(&eb->blocking_writers) != 1);
write_lock(&eb->lock);
@ -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)
{
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 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb)
}
atomic_inc(&eb->write_locks);
atomic_inc(&eb->spinning_writers);
eb->lock_owner = current->pid;
return 1;
}
@ -137,6 +167,15 @@ 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);
}
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(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);
WARN_ON(atomic_read(&eb->blocking_readers) == 0);
if (atomic_dec_and_test(&eb->blocking_readers))
@ -181,6 +229,7 @@ again:
WARN_ON(atomic_read(&eb->spinning_writers));
atomic_inc(&eb->spinning_writers);
atomic_inc(&eb->write_locks);
eb->lock_owner = current->pid;
return 0;
}