@@ -54,8 +54,13 @@ noinline void btrfs_set_path_blocking(struct btrfs_path *p)
{
int i;
for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
- if (p->nodes[i] && p->locks[i])
- btrfs_set_lock_blocking(p->nodes[i]);
+ if (!p->nodes[i] || !p->locks[i])
+ continue;
+ btrfs_set_lock_blocking_rw(p->nodes[i], p->locks[i]);
+ if (p->locks[i] == BTRFS_READ_LOCK)
+ p->locks[i] = BTRFS_READ_LOCK_BLOCKING;
+ else if (p->locks[i] == BTRFS_WRITE_LOCK)
+ p->locks[i] = BTRFS_WRITE_LOCK_BLOCKING;
}
}
@@ -68,7 +73,7 @@ noinline void btrfs_set_path_blocking(struct btrfs_path *p)
* for held
*/
noinline void btrfs_clear_path_blocking(struct btrfs_path *p,
- struct extent_buffer *held)
+ struct extent_buffer *held, int held_rw)
{
int i;
@@ -80,18 +85,23 @@ noinline void btrfs_clear_path_blocking(struct btrfs_path *p,
* the path blocking.
*/
if (held)
- btrfs_set_lock_blocking(held);
+ btrfs_set_lock_blocking_rw(held, held_rw);
btrfs_set_path_blocking(p);
#endif
for (i = BTRFS_MAX_LEVEL - 1; i >= 0; i--) {
- if (p->nodes[i] && p->locks[i])
- btrfs_clear_lock_blocking(p->nodes[i]);
+ if (p->nodes[i] && p->locks[i]) {
+ btrfs_clear_lock_blocking_rw(p->nodes[i], p->locks[i]);
+ if (p->locks[i] == BTRFS_WRITE_LOCK_BLOCKING)
+ p->locks[i] = BTRFS_WRITE_LOCK;
+ else if (p->locks[i] == BTRFS_READ_LOCK_BLOCKING)
+ p->locks[i] = BTRFS_READ_LOCK;
+ }
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
if (held)
- btrfs_clear_lock_blocking(held);
+ btrfs_clear_lock_blocking_rw(held, held_rw);
#endif
}
@@ -119,7 +129,7 @@ noinline void btrfs_release_path(struct btrfs_path *p)
if (!p->nodes[i])
continue;
if (p->locks[i]) {
- btrfs_tree_unlock(p->nodes[i]);
+ btrfs_tree_unlock_rw(p->nodes[i], p->locks[i]);
p->locks[i] = 0;
}
free_extent_buffer(p->nodes[i]);
@@ -167,6 +177,25 @@ struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
return eb;
}
+/* loop around taking references on and locking the root node of the
+ * tree until you end up with a lock on the root. A locked buffer
+ * is returned, with a reference held.
+ */
+struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
+{
+ struct extent_buffer *eb;
+
+ while (1) {
+ eb = btrfs_root_node(root);
+ btrfs_tree_read_lock(eb);
+ if (eb == root->node)
+ break;
+ btrfs_tree_read_unlock(eb);
+ free_extent_buffer(eb);
+ }
+ return eb;
+}
+
/* cowonly root (everything not a reference counted cow subvolume), just get
* put onto a simple dirty list. transaction.c walks this to make sure they
* get properly updated on disk.
@@ -862,7 +891,8 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
mid = path->nodes[level];
- WARN_ON(!path->locks[level]);
+ WARN_ON(path->locks[level] != BTRFS_WRITE_LOCK &&
+ path->locks[level] != BTRFS_WRITE_LOCK_BLOCKING);
WARN_ON(btrfs_header_generation(mid) != trans->transid);
orig_ptr = btrfs_node_blockptr(mid, orig_slot);
@@ -1360,7 +1390,7 @@ static noinline void unlock_up(struct btrfs_path *path, int level,
t = path->nodes[i];
if (i >= lowest_unlock && i > skip_level && path->locks[i]) {
- btrfs_tree_unlock(t);
+ btrfs_tree_unlock_rw(t, path->locks[i]);
path->locks[i] = 0;
}
}
@@ -1387,7 +1417,7 @@ noinline void btrfs_unlock_up_safe(struct btrfs_path *path, int level)
continue;
if (!path->locks[i])
continue;
- btrfs_tree_unlock(path->nodes[i]);
+ btrfs_tree_unlock_rw(path->nodes[i], path->locks[i]);
path->locks[i] = 0;
}
}
@@ -1436,6 +1466,8 @@ read_block_for_search(struct btrfs_trans_handle *trans,
* we can trust our generation number
*/
free_extent_buffer(tmp);
+ btrfs_set_path_blocking(p);
+
tmp = read_tree_block(root, blocknr, blocksize, gen);
if (tmp && btrfs_buffer_uptodate(tmp, gen)) {
*eb_ret = tmp;
@@ -1491,20 +1523,27 @@ read_block_for_search(struct btrfs_trans_handle *trans,
static int
setup_nodes_for_search(struct btrfs_trans_handle *trans,
struct btrfs_root *root, struct btrfs_path *p,
- struct extent_buffer *b, int level, int ins_len)
+ struct extent_buffer *b, int level, int ins_len,
+ int *write_lock_level)
{
int ret;
if ((p->search_for_split || ins_len > 0) && btrfs_header_nritems(b) >=
BTRFS_NODEPTRS_PER_BLOCK(root) - 3) {
int sret;
+ if (*write_lock_level < level + 1) {
+ *write_lock_level = level + 1;
+ btrfs_release_path(p);
+ goto again;
+ }
+
sret = reada_for_balance(root, p, level);
if (sret)
goto again;
btrfs_set_path_blocking(p);
sret = split_node(trans, root, p, level);
- btrfs_clear_path_blocking(p, NULL);
+ btrfs_clear_path_blocking(p, NULL, 0);
BUG_ON(sret > 0);
if (sret) {
@@ -1516,13 +1555,19 @@ setup_nodes_for_search(struct btrfs_trans_handle *trans,
BTRFS_NODEPTRS_PER_BLOCK(root) / 2) {
int sret;
+ if (*write_lock_level < level + 1) {
+ *write_lock_level = level + 1;
+ btrfs_release_path(p);
+ goto again;
+ }
+
sret = reada_for_balance(root, p, level);
if (sret)
goto again;
btrfs_set_path_blocking(p);
sret = balance_level(trans, root, p, level);
- btrfs_clear_path_blocking(p, NULL);
+ btrfs_clear_path_blocking(p, NULL, 0);
if (sret) {
ret = sret;
@@ -1566,27 +1611,78 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
int err;
int level;
int lowest_unlock = 1;
+ int root_lock;
+ /* everything at write_lock_level or lower must be write locked */
+ int write_lock_level = 0;
u8 lowest_level = 0;
lowest_level = p->lowest_level;
WARN_ON(lowest_level && ins_len > 0);
WARN_ON(p->nodes[0] != NULL);
- if (ins_len < 0)
+ if (ins_len < 0) {
lowest_unlock = 2;
+ /* when we are removing items, we might have to go up to level
+ * two as we update tree pointers Make sure we keep write
+ * for those levels as well
+ */
+ write_lock_level = 2;
+ } else if (ins_len > 0) {
+ /*
+ * for inserting items, make sure we have a write lock on
+ * level 1 so we can update keys
+ */
+ write_lock_level = 1;
+ }
+
+ if (!cow)
+ write_lock_level = -1;
+
+ if (cow && (p->keep_locks || p->lowest_level))
+ write_lock_level = BTRFS_MAX_LEVEL;
+
again:
+ /*
+ * we try very hard to do read locks on the root
+ */
+ root_lock = BTRFS_READ_LOCK;
+ level = 0;
if (p->search_commit_root) {
+ /*
+ * the commit roots are read only
+ * so we always do read locks
+ */
b = root->commit_root;
extent_buffer_get(b);
+ level = btrfs_header_level(b);
if (!p->skip_locking)
- btrfs_tree_lock(b);
+ btrfs_tree_read_lock(b);
} else {
- if (p->skip_locking)
+ if (p->skip_locking) {
b = btrfs_root_node(root);
- else
- b = btrfs_lock_root_node(root);
+ level = btrfs_header_level(b);
+ } else {
+ /* we don't know the level of the root node
+ * until we actually have it read locked
+ */
+ b = btrfs_read_lock_root_node(root);
+ level = btrfs_header_level(b);
+ if (level <= write_lock_level) {
+ /* whoops, must trade for write lock */
+ btrfs_tree_read_unlock(b);
+ free_extent_buffer(b);
+ b = btrfs_lock_root_node(root);
+ root_lock = BTRFS_WRITE_LOCK;
+
+ /* the level might have changed, check again */
+ level = btrfs_header_level(b);
+ }
+ }
}
+ p->nodes[level] = b;
+ if (!p->skip_locking)
+ p->locks[level] = root_lock;
while (b) {
level = btrfs_header_level(b);
@@ -1595,10 +1691,6 @@ again:
* setup the path here so we can release it under lock
* contention with the cow code
*/
- p->nodes[level] = b;
- if (!p->skip_locking)
- p->locks[level] = 1;
-
if (cow) {
/*
* if we don't really need to cow this block
@@ -1610,6 +1702,16 @@ again:
btrfs_set_path_blocking(p);
+ /*
+ * must have write locks on this node and the
+ * parent
+ */
+ if (level + 1 > write_lock_level) {
+ write_lock_level = level + 1;
+ btrfs_release_path(p);
+ goto again;
+ }
+
err = btrfs_cow_block(trans, root, b,
p->nodes[level + 1],
p->slots[level + 1], &b);
@@ -1622,10 +1724,7 @@ cow_done:
BUG_ON(!cow && ins_len);
p->nodes[level] = b;
- if (!p->skip_locking)
- p->locks[level] = 1;
-
- btrfs_clear_path_blocking(p, NULL);
+ btrfs_clear_path_blocking(p, NULL, 0);
/*
* we have a lock on b and as long as we aren't changing
@@ -1651,7 +1750,7 @@ cow_done:
}
p->slots[level] = slot;
err = setup_nodes_for_search(trans, root, p, b, level,
- ins_len);
+ ins_len, &write_lock_level);
if (err == -EAGAIN)
goto again;
if (err) {
@@ -1661,6 +1760,19 @@ cow_done:
b = p->nodes[level];
slot = p->slots[level];
+ /*
+ * slot 0 is special, if we change the key
+ * we have to update the parent pointer
+ * which means we must have a write lock
+ * on the parent
+ */
+ if (slot == 0 && cow &&
+ write_lock_level < level + 1) {
+ write_lock_level = level + 1;
+ btrfs_release_path(p);
+ goto again;
+ }
+
unlock_up(p, level, lowest_unlock);
if (level == lowest_level) {
@@ -1679,23 +1791,42 @@ cow_done:
}
if (!p->skip_locking) {
- btrfs_clear_path_blocking(p, NULL);
- err = btrfs_try_spin_lock(b);
-
- if (!err) {
- btrfs_set_path_blocking(p);
- btrfs_tree_lock(b);
- btrfs_clear_path_blocking(p, b);
+ level = btrfs_header_level(b);
+ if (level <= write_lock_level) {
+ err = btrfs_try_tree_write_lock(b);
+ if (!err) {
+ btrfs_set_path_blocking(p);
+ btrfs_tree_lock(b);
+ btrfs_clear_path_blocking(p, b,
+ BTRFS_WRITE_LOCK);
+ }
+ p->locks[level] = BTRFS_WRITE_LOCK;
+ } else {
+ err = btrfs_try_tree_read_lock(b);
+ if (!err) {
+ btrfs_set_path_blocking(p);
+ btrfs_tree_read_lock(b);
+ btrfs_clear_path_blocking(p, b,
+ BTRFS_READ_LOCK);
+ }
+ p->locks[level] = BTRFS_READ_LOCK;
}
+ p->nodes[level] = b;
}
} else {
p->slots[level] = slot;
if (ins_len > 0 &&
btrfs_leaf_free_space(root, b) < ins_len) {
+ if (write_lock_level < 1) {
+ write_lock_level = 1;
+ btrfs_release_path(p);
+ goto again;
+ }
+
btrfs_set_path_blocking(p);
err = split_leaf(trans, root, key,
p, ins_len, ret == 0);
- btrfs_clear_path_blocking(p, NULL);
+ btrfs_clear_path_blocking(p, NULL, 0);
BUG_ON(err > 0);
if (err) {
@@ -1976,7 +2107,7 @@ static noinline int insert_new_root(struct btrfs_trans_handle *trans,
add_root_to_dirty_list(root);
extent_buffer_get(c);
path->nodes[level] = c;
- path->locks[level] = 1;
+ path->locks[level] = BTRFS_WRITE_LOCK;
path->slots[level] = 0;
return 0;
}
@@ -3819,11 +3950,11 @@ int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
WARN_ON(!path->keep_locks);
again:
- cur = btrfs_lock_root_node(root);
+ cur = btrfs_read_lock_root_node(root);
level = btrfs_header_level(cur);
WARN_ON(path->nodes[level]);
path->nodes[level] = cur;
- path->locks[level] = 1;
+ path->locks[level] = BTRFS_READ_LOCK;
if (btrfs_header_generation(cur) < min_trans) {
ret = 1;
@@ -3913,12 +4044,12 @@ find_next_key:
cur = read_node_slot(root, cur, slot);
BUG_ON(!cur);
- btrfs_tree_lock(cur);
+ btrfs_tree_read_lock(cur);
- path->locks[level - 1] = 1;
+ path->locks[level - 1] = BTRFS_READ_LOCK;
path->nodes[level - 1] = cur;
unlock_up(path, level, 1);
- btrfs_clear_path_blocking(path, NULL);
+ btrfs_clear_path_blocking(path, NULL, 0);
}
out:
if (ret == 0)
@@ -4034,6 +4165,7 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
int ret;
int old_spinning = path->leave_spinning;
int force_blocking = 0;
+ int next_rw_lock = 0;
nritems = btrfs_header_nritems(path->nodes[0]);
if (nritems == 0)
@@ -4051,6 +4183,7 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
again:
level = 1;
next = NULL;
+ next_rw_lock = 0;
btrfs_release_path(path);
path->keep_locks = 1;
@@ -4096,11 +4229,12 @@ again:
}
if (next) {
- btrfs_tree_unlock(next);
+ btrfs_tree_unlock_rw(next, next_rw_lock);
free_extent_buffer(next);
}
next = c;
+ next_rw_lock = path->locks[level];
ret = read_block_for_search(NULL, root, path, &next, level,
slot, &key);
if (ret == -EAGAIN)
@@ -4112,15 +4246,22 @@ again:
}
if (!path->skip_locking) {
- ret = btrfs_try_spin_lock(next);
+ ret = btrfs_try_tree_read_lock(next);
if (!ret) {
btrfs_set_path_blocking(path);
- btrfs_tree_lock(next);
- if (!force_blocking)
- btrfs_clear_path_blocking(path, next);
+ btrfs_tree_read_lock(next);
+ if (!force_blocking) {
+ btrfs_clear_path_blocking(path, next,
+ BTRFS_READ_LOCK);
+ }
+ }
+ if (force_blocking) {
+ btrfs_set_lock_blocking_rw(next,
+ BTRFS_READ_LOCK);
+ next_rw_lock = BTRFS_READ_LOCK_BLOCKING;
+ } else {
+ next_rw_lock = BTRFS_READ_LOCK;
}
- if (force_blocking)
- btrfs_set_lock_blocking(next);
}
break;
}
@@ -4129,14 +4270,13 @@ again:
level--;
c = path->nodes[level];
if (path->locks[level])
- btrfs_tree_unlock(c);
+ btrfs_tree_unlock_rw(c, path->locks[level]);
free_extent_buffer(c);
path->nodes[level] = next;
path->slots[level] = 0;
if (!path->skip_locking)
- path->locks[level] = 1;
-
+ path->locks[level] = next_rw_lock;
if (!level)
break;
@@ -4151,16 +4291,21 @@ again:
}
if (!path->skip_locking) {
- btrfs_assert_tree_locked(path->nodes[level]);
- ret = btrfs_try_spin_lock(next);
+ ret = btrfs_try_tree_read_lock(next);
if (!ret) {
btrfs_set_path_blocking(path);
- btrfs_tree_lock(next);
+ btrfs_tree_read_lock(next);
if (!force_blocking)
- btrfs_clear_path_blocking(path, next);
+ btrfs_clear_path_blocking(path, next,
+ BTRFS_READ_LOCK);
+ }
+ if (force_blocking) {
+ btrfs_set_lock_blocking_rw(next,
+ BTRFS_READ_LOCK);
+ next_rw_lock = BTRFS_READ_LOCK_BLOCKING;
+ } else {
+ next_rw_lock = BTRFS_READ_LOCK;
}
- if (force_blocking)
- btrfs_set_lock_blocking(next);
}
}
ret = 0;
@@ -2333,7 +2333,7 @@ struct btrfs_path *btrfs_alloc_path(void);
void btrfs_free_path(struct btrfs_path *p);
void btrfs_set_path_blocking(struct btrfs_path *p);
void btrfs_clear_path_blocking(struct btrfs_path *p,
- struct extent_buffer *held);
+ struct extent_buffer *held, int held_rw);
void btrfs_unlock_up_safe(struct btrfs_path *p, int level);
int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
@@ -735,7 +735,7 @@ static int btrfs_batch_insert_items(struct btrfs_trans_handle *trans,
}
/* reset all the locked nodes in the patch to spinning locks. */
- btrfs_clear_path_blocking(path, NULL);
+ btrfs_clear_path_blocking(path, NULL, 0);
/* insert the keys of the items */
ret = setup_items_for_insert(trans, root, path, keys, data_size,
@@ -5919,7 +5919,7 @@ static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
return 1;
if (path->locks[level] && !wc->keep_locks) {
- btrfs_tree_unlock(eb);
+ btrfs_tree_unlock_rw(eb, path->locks[level]);
path->locks[level] = 0;
}
return 0;
@@ -5943,7 +5943,7 @@ static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
* keep the tree lock
*/
if (path->locks[level] && level > 0) {
- btrfs_tree_unlock(eb);
+ btrfs_tree_unlock_rw(eb, path->locks[level]);
path->locks[level] = 0;
}
return 0;
@@ -6056,7 +6056,7 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
BUG_ON(level != btrfs_header_level(next));
path->nodes[level] = next;
path->slots[level] = 0;
- path->locks[level] = 1;
+ path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
wc->level = level;
if (wc->level == 1)
wc->reada_slot = 0;
@@ -6127,7 +6127,7 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
BUG_ON(level == 0);
btrfs_tree_lock(eb);
btrfs_set_lock_blocking(eb);
- path->locks[level] = 1;
+ path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
ret = btrfs_lookup_extent_info(trans, root,
eb->start, eb->len,
@@ -6136,8 +6136,7 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
BUG_ON(ret);
BUG_ON(wc->refs[level] == 0);
if (wc->refs[level] == 1) {
- btrfs_tree_unlock(eb);
- path->locks[level] = 0;
+ btrfs_tree_unlock_rw(eb, path->locks[level]);
return 1;
}
}
@@ -6159,7 +6158,7 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
btrfs_header_generation(eb) == trans->transid) {
btrfs_tree_lock(eb);
btrfs_set_lock_blocking(eb);
- path->locks[level] = 1;
+ path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
}
clean_tree_block(trans, root, eb);
}
@@ -6238,7 +6237,8 @@ static noinline int walk_up_tree(struct btrfs_trans_handle *trans,
return 0;
if (path->locks[level]) {
- btrfs_tree_unlock(path->nodes[level]);
+ btrfs_tree_unlock_rw(path->nodes[level],
+ path->locks[level]);
path->locks[level] = 0;
}
free_extent_buffer(path->nodes[level]);
@@ -6290,7 +6290,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
path->nodes[level] = btrfs_lock_root_node(root);
btrfs_set_lock_blocking(path->nodes[level]);
path->slots[level] = 0;
- path->locks[level] = 1;
+ path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
memset(&wc->update_progress, 0,
sizeof(wc->update_progress));
} else {
@@ -6458,7 +6458,7 @@ int btrfs_drop_subtree(struct btrfs_trans_handle *trans,
level = btrfs_header_level(node);
path->nodes[level] = node;
path->slots[level] = 0;
- path->locks[level] = 1;
+ path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
wc->refs[parent_level] = 1;
wc->flags[parent_level] = BTRFS_BLOCK_FLAG_FULL_BACKREF;
@@ -3017,8 +3017,15 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
return NULL;
eb->start = start;
eb->len = len;
- spin_lock_init(&eb->lock);
- init_waitqueue_head(&eb->lock_wq);
+ rwlock_init(&eb->lock);
+ atomic_set(&eb->write_locks, 0);
+ atomic_set(&eb->read_locks, 0);
+ atomic_set(&eb->blocking_readers, 0);
+ atomic_set(&eb->blocking_writers, 0);
+ atomic_set(&eb->spinning_readers, 0);
+ atomic_set(&eb->spinning_writers, 0);
+ init_waitqueue_head(&eb->write_lock_wq);
+ init_waitqueue_head(&eb->read_lock_wq);
#if LEAK_DEBUG
spin_lock_irqsave(&leak_lock, flags);
@@ -128,14 +128,26 @@ struct extent_buffer {
struct rcu_head rcu_head;
atomic_t refs;
- /* the spinlock is used to protect most operations */
- spinlock_t lock;
+ /* count of read lock holders on the extent buffer */
+ atomic_t write_locks;
+ atomic_t read_locks;
+ atomic_t blocking_writers;
+ atomic_t blocking_readers;
+ atomic_t spinning_readers;
+ atomic_t spinning_writers;
+
+ /* protects write locks */
+ rwlock_t lock;
+
+ /* readers use lock_wq while they wait for the write
+ * lock holders to unlock
+ */
+ wait_queue_head_t write_lock_wq;
- /*
- * when we keep the lock held while blocking, waiters go onto
- * the wq
+ /* writers use read_lock_wq while they wait for readers
+ * to unlock
*/
- wait_queue_head_t lock_wq;
+ wait_queue_head_t read_lock_wq;
};
static inline void extent_set_compress_type(unsigned long *bio_flags,
@@ -24,185 +24,197 @@
#include "extent_io.h"
#include "locking.h"
-static inline void spin_nested(struct extent_buffer *eb)
-{
- spin_lock(&eb->lock);
-}
+void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
/*
- * Setting a lock to blocking will drop the spinlock and set the
- * flag that forces other procs who want the lock to wait. After
- * this you can safely schedule with the lock held.
+ * if we currently have a spinning reader or writer lock
+ * (indicated by the rw flag) this will bump the count
+ * of blocking holders and drop the spinlock.
*/
-void btrfs_set_lock_blocking(struct extent_buffer *eb)
+void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
{
- if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) {
- set_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags);
- spin_unlock(&eb->lock);
+ if (rw == BTRFS_WRITE_LOCK) {
+ if (atomic_read(&eb->blocking_writers) == 0) {
+ WARN_ON(atomic_read(&eb->spinning_writers) != 1);
+ atomic_dec(&eb->spinning_writers);
+ btrfs_assert_tree_locked(eb);
+ atomic_inc(&eb->blocking_writers);
+ write_unlock(&eb->lock);
+ }
+ } else if (rw == BTRFS_READ_LOCK) {
+ btrfs_assert_tree_read_locked(eb);
+ atomic_inc(&eb->blocking_readers);
+ WARN_ON(atomic_read(&eb->spinning_readers) == 0);
+ atomic_dec(&eb->spinning_readers);
+ read_unlock(&eb->lock);
}
- /* exit with the spin lock released and the bit set */
+ return;
}
/*
- * clearing the blocking flag will take the spinlock again.
- * After this you can't safely schedule
+ * if we currently have a blocking lock, take the spinlock
+ * and drop our blocking count
*/
-void btrfs_clear_lock_blocking(struct extent_buffer *eb)
+void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
{
- if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) {
- spin_nested(eb);
- clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags);
- smp_mb__after_clear_bit();
+ if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
+ BUG_ON(atomic_read(&eb->blocking_writers) != 1);
+ write_lock(&eb->lock);
+ WARN_ON(atomic_read(&eb->spinning_writers));
+ atomic_inc(&eb->spinning_writers);
+ if (atomic_dec_and_test(&eb->blocking_writers))
+ wake_up(&eb->write_lock_wq);
+ } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
+ BUG_ON(atomic_read(&eb->blocking_readers) == 0);
+ read_lock(&eb->lock);
+ atomic_inc(&eb->spinning_readers);
+ if (atomic_dec_and_test(&eb->blocking_readers))
+ wake_up(&eb->read_lock_wq);
}
- /* exit with the spin lock held */
+ return;
}
/*
- * unfortunately, many of the places that currently set a lock to blocking
- * don't end up blocking for very long, and often they don't block
- * at all. For a dbench 50 run, if we don't spin on the blocking bit
- * at all, the context switch rate can jump up to 400,000/sec or more.
- *
- * So, we're still stuck with this crummy spin on the blocking bit,
- * at least until the most common causes of the short blocks
- * can be dealt with.
+ * take a spinning read lock. This will wait for any blocking
+ * writers
*/
-static int btrfs_spin_on_block(struct extent_buffer *eb)
+void btrfs_tree_read_lock(struct extent_buffer *eb)
{
- int i;
-
- for (i = 0; i < 512; i++) {
- if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
- return 1;
- if (need_resched())
- break;
- cpu_relax();
+again:
+ 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;
}
- return 0;
+ atomic_inc(&eb->read_locks);
+ atomic_inc(&eb->spinning_readers);
}
/*
- * This is somewhat different from trylock. It will take the
- * spinlock but if it finds the lock is set to blocking, it will
- * return without the lock held.
- *
- * returns 1 if it was able to take the lock and zero otherwise
- *
- * After this call, scheduling is not safe without first calling
- * btrfs_set_lock_blocking()
+ * returns 1 if we get the read lock and 0 if we don't
+ * this won't wait for blocking writers
*/
-int btrfs_try_spin_lock(struct extent_buffer *eb)
+int btrfs_try_tree_read_lock(struct extent_buffer *eb)
{
- int i;
+ if (atomic_read(&eb->blocking_writers))
+ return 0;
- if (btrfs_spin_on_block(eb)) {
- spin_nested(eb);
- if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
- return 1;
- spin_unlock(&eb->lock);
+ read_lock(&eb->lock);
+ if (atomic_read(&eb->blocking_writers)) {
+ read_unlock(&eb->lock);
+ return 0;
}
- /* spin for a bit on the BLOCKING flag */
- for (i = 0; i < 2; i++) {
- cpu_relax();
- if (!btrfs_spin_on_block(eb))
- break;
-
- spin_nested(eb);
- if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
- return 1;
- spin_unlock(&eb->lock);
- }
- return 0;
+ atomic_inc(&eb->read_locks);
+ atomic_inc(&eb->spinning_readers);
+ return 1;
}
/*
- * the autoremove wake function will return 0 if it tried to wake up
- * a process that was already awake, which means that process won't
- * count as an exclusive wakeup. The waitq code will continue waking
- * procs until it finds one that was actually sleeping.
- *
- * For btrfs, this isn't quite what we want. We want a single proc
- * to be notified that the lock is ready for taking. If that proc
- * already happen to be awake, great, it will loop around and try for
- * the lock.
- *
- * So, btrfs_wake_function always returns 1, even when the proc that we
- * tried to wake up was already awake.
+ * returns 1 if we get the read lock and 0 if we don't
+ * this won't wait for blocking writers or readers
*/
-static int btrfs_wake_function(wait_queue_t *wait, unsigned mode,
- int sync, void *key)
+int btrfs_try_tree_write_lock(struct extent_buffer *eb)
{
- autoremove_wake_function(wait, mode, sync, key);
+ if (atomic_read(&eb->blocking_writers) ||
+ atomic_read(&eb->blocking_readers))
+ return 0;
+ write_lock(&eb->lock);
+ if (atomic_read(&eb->blocking_writers) ||
+ atomic_read(&eb->blocking_readers)) {
+ write_unlock(&eb->lock);
+ return 0;
+ }
+ atomic_inc(&eb->write_locks);
+ atomic_inc(&eb->spinning_writers);
return 1;
}
/*
- * returns with the extent buffer spinlocked.
- *
- * This will spin and/or wait as required to take the lock, and then
- * return with the spinlock held.
- *
- * After this call, scheduling is not safe without first calling
- * btrfs_set_lock_blocking()
+ * drop a spinning read lock
+ */
+void btrfs_tree_read_unlock(struct extent_buffer *eb)
+{
+ btrfs_assert_tree_read_locked(eb);
+ WARN_ON(atomic_read(&eb->spinning_readers) == 0);
+ atomic_dec(&eb->spinning_readers);
+ atomic_dec(&eb->read_locks);
+ read_unlock(&eb->lock);
+}
+
+/*
+ * drop a blocking read lock
+ */
+void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
+{
+ btrfs_assert_tree_read_locked(eb);
+ WARN_ON(atomic_read(&eb->blocking_readers) == 0);
+ if (atomic_dec_and_test(&eb->blocking_readers))
+ wake_up(&eb->read_lock_wq);
+ atomic_dec(&eb->read_locks);
+}
+
+/*
+ * take a spinning write lock. This will wait for both
+ * blocking readers or writers
*/
int btrfs_tree_lock(struct extent_buffer *eb)
{
- DEFINE_WAIT(wait);
- wait.func = btrfs_wake_function;
-
- if (!btrfs_spin_on_block(eb))
- goto sleep;
-
- while(1) {
- spin_nested(eb);
-
- /* nobody is blocking, exit with the spinlock held */
- if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
- return 0;
-
- /*
- * we have the spinlock, but the real owner is blocking.
- * wait for them
- */
- spin_unlock(&eb->lock);
-
- /*
- * spin for a bit, and if the blocking flag goes away,
- * loop around
- */
- cpu_relax();
- if (btrfs_spin_on_block(eb))
- continue;
-sleep:
- prepare_to_wait_exclusive(&eb->lock_wq, &wait,
- TASK_UNINTERRUPTIBLE);
-
- if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
- schedule();
-
- finish_wait(&eb->lock_wq, &wait);
+again:
+ wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
+ wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
+ write_lock(&eb->lock);
+ if (atomic_read(&eb->blocking_readers)) {
+ write_unlock(&eb->lock);
+ wait_event(eb->read_lock_wq,
+ atomic_read(&eb->blocking_readers) == 0);
+ goto again;
}
+ if (atomic_read(&eb->blocking_writers)) {
+ write_unlock(&eb->lock);
+ wait_event(eb->write_lock_wq,
+ atomic_read(&eb->blocking_writers) == 0);
+ goto again;
+ }
+ WARN_ON(atomic_read(&eb->spinning_writers));
+ atomic_inc(&eb->spinning_writers);
+ atomic_inc(&eb->write_locks);
return 0;
}
+/*
+ * drop a spinning or a blocking write lock.
+ */
int btrfs_tree_unlock(struct extent_buffer *eb)
{
- /*
- * if we were a blocking owner, we don't have the spinlock held
- * just clear the bit and look for waiters
- */
- if (test_and_clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
- smp_mb__after_clear_bit();
- else
- spin_unlock(&eb->lock);
-
- if (waitqueue_active(&eb->lock_wq))
- wake_up(&eb->lock_wq);
+ int blockers = atomic_read(&eb->blocking_writers);
+
+ BUG_ON(blockers > 1);
+
+ btrfs_assert_tree_locked(eb);
+ atomic_dec(&eb->write_locks);
+
+ if (blockers) {
+ WARN_ON(atomic_read(&eb->spinning_writers));
+ atomic_dec(&eb->blocking_writers);
+ smp_wmb();
+ wake_up(&eb->write_lock_wq);
+ } else {
+ WARN_ON(atomic_read(&eb->spinning_writers) != 1);
+ atomic_dec(&eb->spinning_writers);
+ write_unlock(&eb->lock);
+ }
return 0;
}
void btrfs_assert_tree_locked(struct extent_buffer *eb)
{
- if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
- assert_spin_locked(&eb->lock);
+ BUG_ON(!atomic_read(&eb->write_locks));
+}
+
+void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
+{
+ BUG_ON(!atomic_read(&eb->read_locks));
}
@@ -19,11 +19,43 @@
#ifndef __BTRFS_LOCKING_
#define __BTRFS_LOCKING_
+#define BTRFS_WRITE_LOCK 1
+#define BTRFS_READ_LOCK 2
+#define BTRFS_WRITE_LOCK_BLOCKING 3
+#define BTRFS_READ_LOCK_BLOCKING 4
+
int btrfs_tree_lock(struct extent_buffer *eb);
int btrfs_tree_unlock(struct extent_buffer *eb);
int btrfs_try_spin_lock(struct extent_buffer *eb);
-void btrfs_set_lock_blocking(struct extent_buffer *eb);
-void btrfs_clear_lock_blocking(struct extent_buffer *eb);
+void btrfs_tree_read_lock(struct extent_buffer *eb);
+void btrfs_tree_read_unlock(struct extent_buffer *eb);
+void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb);
+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_assert_tree_locked(struct extent_buffer *eb);
+int btrfs_try_tree_read_lock(struct extent_buffer *eb);
+int btrfs_try_tree_write_lock(struct extent_buffer *eb);
+
+static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
+{
+ if (rw == BTRFS_WRITE_LOCK || rw == BTRFS_WRITE_LOCK_BLOCKING)
+ btrfs_tree_unlock(eb);
+ else if (rw == BTRFS_READ_LOCK_BLOCKING)
+ btrfs_tree_read_unlock_blocking(eb);
+ else if (rw == BTRFS_READ_LOCK)
+ btrfs_tree_read_unlock(eb);
+ else
+ BUG();
+}
+
+static inline void btrfs_set_lock_blocking(struct extent_buffer *eb)
+{
+ btrfs_set_lock_blocking_rw(eb, BTRFS_WRITE_LOCK);
+}
+
+static inline void btrfs_clear_lock_blocking(struct extent_buffer *eb)
+{
+ btrfs_clear_lock_blocking_rw(eb, BTRFS_WRITE_LOCK_BLOCKING);
+}
#endif
@@ -1730,8 +1730,8 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
btrfs_read_buffer(next, ptr_gen);
btrfs_tree_lock(next);
- clean_tree_block(trans, root, next);
btrfs_set_lock_blocking(next);
+ clean_tree_block(trans, root, next);
btrfs_wait_tree_block_writeback(next);
btrfs_tree_unlock(next);
@@ -1796,8 +1796,8 @@ static noinline int walk_up_log_tree(struct btrfs_trans_handle *trans,
next = path->nodes[*level];
btrfs_tree_lock(next);
- clean_tree_block(trans, root, next);
btrfs_set_lock_blocking(next);
+ clean_tree_block(trans, root, next);
btrfs_wait_tree_block_writeback(next);
btrfs_tree_unlock(next);
@@ -1864,8 +1864,8 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
next = path->nodes[orig_level];
btrfs_tree_lock(next);
- clean_tree_block(trans, log, next);
btrfs_set_lock_blocking(next);
+ clean_tree_block(trans, log, next);
btrfs_wait_tree_block_writeback(next);
btrfs_tree_unlock(next);