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Btrfs: Add a skip_locking parameter to struct path, and make various funcs honor it 

Allocations may need to read in block groups from the extent allocation tree,
which will require a tree search and take locks on the extent allocation
tree.  But, those locks might already be held in other places, leading
to deadlocks.

Since the alloc_mutex serializes everything right now, it is safe to
skip the btree locking while caching block groups.  A better fix will be
to either create a recursive lock or find a way to back off existing
locks while caching block groups.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
wifi-calibration
Chris Mason 2008-06-25 16:01:30 -04:00
parent 168fd7d271
commit 5cd57b2cbb
3 changed files with 25 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
fs/btrfs/ctree.c
View File

@ -64,6 +64,7 @@ void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p)
{
int i;
int keep = p->keep_locks;
int skip = p->skip_locking;
for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
if (!p->nodes[i])
@ -76,6 +77,7 @@ void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p)
}
memset(p, 0, sizeof(*p));
p->keep_locks = keep;
p->skip_locking = skip;
}
struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
@ -1262,7 +1264,10 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
if (ins_len < 0)
lowest_unlock = 2;
again:
b = btrfs_lock_root_node(root);
if (p->skip_locking)
b = btrfs_root_node(root);
else
b = btrfs_lock_root_node(root);
while (b) {
level = btrfs_header_level(b);
@ -1282,7 +1287,8 @@ again:
WARN_ON(1);
level = btrfs_header_level(b);
p->nodes[level] = b;
p->locks[level] = 1;
if (!p->skip_locking)
p->locks[level] = 1;
ret = check_block(root, p, level);
if (ret)
return -1;
@ -1349,7 +1355,8 @@ again:
b = read_node_slot(root, b, slot);
}
}
btrfs_tree_lock(b);
if (!p->skip_locking)
btrfs_tree_lock(b);
unlock_up(p, level, lowest_unlock);
} else {
p->slots[level] = slot;
@ -1392,13 +1399,6 @@ static int fixup_low_keys(struct btrfs_trans_handle *trans,
break;
t = path->nodes[i];
btrfs_set_node_key(t, key, tslot);
if (!btrfs_tree_locked(path->nodes[i])) {
int ii;
printk("fixup without lock on level %d\n", btrfs_header_level(path->nodes[i]));
for (ii = 0; ii < BTRFS_MAX_LEVEL; ii++) {
printk("level %d slot %d\n", ii, path->slots[ii]);
}
}
btrfs_mark_buffer_dirty(path->nodes[i]);
if (tslot != 0)
break;
@ -3033,8 +3033,10 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
reada_for_search(root, path, level, slot, 0);
next = read_node_slot(root, c, slot);
WARN_ON(!btrfs_tree_locked(c));
btrfs_tree_lock(next);
if (!path->skip_locking) {
WARN_ON(!btrfs_tree_locked(c));
btrfs_tree_lock(next);
}
break;
}
path->slots[level] = slot;
@ -3052,8 +3054,10 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
if (level == 1 && path->locks[1] && path->reada)
reada_for_search(root, path, level, slot, 0);
next = read_node_slot(root, next, 0);
WARN_ON(!btrfs_tree_locked(path->nodes[level]));
btrfs_tree_lock(next);
if (!path->skip_locking) {
WARN_ON(!btrfs_tree_locked(path->nodes[level]));
btrfs_tree_lock(next);
}
}
done:
unlock_up(path, 0, 1);

1
fs/btrfs/ctree.h
View File

@ -335,6 +335,7 @@ struct btrfs_path {
int reada;
/* keep some upper locks as we walk down */
int keep_locks;
int skip_locking;
int lowest_level;
};

6
fs/btrfs/extent-tree.c
View File

@ -88,6 +88,12 @@ static int cache_block_group(struct btrfs_root *root,
return -ENOMEM;
path->reada = 2;
/*
* we get into deadlocks with paths held by callers of this function.
* since the alloc_mutex is protecting things right now, just
* skip the locking here
*/
path->skip_locking = 1;
first_free = block_group->key.objectid;
key.objectid = block_group->key.objectid;
key.offset = 0;