Btrfs: deal with convert_extent_bit errors to avoid fs corruption
When committing a transaction or a log, we look for btree extents that
need to be durably persisted by searching for ranges in a io tree that
have some bits set (EXTENT_DIRTY or EXTENT_NEW). We then attempt to clear
those bits and set the EXTENT_NEED_WAIT bit, with calls to the function
convert_extent_bit, and then start writeback for the extents.
That function however can return an error (at the moment only -ENOMEM
is possible, specially when it does GFP_ATOMIC allocation requests
through alloc_extent_state_atomic) - that means the ranges didn't got
the EXTENT_NEED_WAIT bit set (or at least not for the whole range),
which in turn means a call to btrfs_wait_marked_extents() won't find
those ranges for which we started writeback, causing a transaction
commit or a log commit to persist a new superblock without waiting
for the writeback of extents in that range to finish first.
Therefore if a crash happens after persisting the new superblock and
before writeback finishes, we have a superblock pointing to roots that
weren't fully persisted or roots that point to nodes or leafs that weren't
fully persisted, causing all sorts of unexpected/bad behaviour as we endup
reading garbage from disk or the content of some node/leaf from a past
generation that got cowed or deleted and is no longer valid (for this later
case we end up getting error messages like "parent transid verify failed on
X wanted Y found Z" when reading btree nodes/leafs from disk).
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index dcaae36..04dbc80 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -76,6 +76,32 @@
}
}
+static void clear_btree_io_tree(struct extent_io_tree *tree)
+{
+ spin_lock(&tree->lock);
+ while (!RB_EMPTY_ROOT(&tree->state)) {
+ struct rb_node *node;
+ struct extent_state *state;
+
+ node = rb_first(&tree->state);
+ state = rb_entry(node, struct extent_state, rb_node);
+ rb_erase(&state->rb_node, &tree->state);
+ RB_CLEAR_NODE(&state->rb_node);
+ /*
+ * btree io trees aren't supposed to have tasks waiting for
+ * changes in the flags of extent states ever.
+ */
+ ASSERT(!waitqueue_active(&state->wq));
+ free_extent_state(state);
+ if (need_resched()) {
+ spin_unlock(&tree->lock);
+ cond_resched();
+ spin_lock(&tree->lock);
+ }
+ }
+ spin_unlock(&tree->lock);
+}
+
static noinline void switch_commit_roots(struct btrfs_transaction *trans,
struct btrfs_fs_info *fs_info)
{
@@ -89,6 +115,7 @@
root->commit_root = btrfs_root_node(root);
if (is_fstree(root->objectid))
btrfs_unpin_free_ino(root);
+ clear_btree_io_tree(&root->dirty_log_pages);
}
up_write(&fs_info->commit_root_sem);
}
@@ -828,17 +855,38 @@
while (!find_first_extent_bit(dirty_pages, start, &start, &end,
mark, &cached_state)) {
- convert_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
- mark, &cached_state, GFP_NOFS);
- cached_state = NULL;
- err = filemap_fdatawrite_range(mapping, start, end);
+ bool wait_writeback = false;
+
+ err = convert_extent_bit(dirty_pages, start, end,
+ EXTENT_NEED_WAIT,
+ mark, &cached_state, GFP_NOFS);
+ /*
+ * convert_extent_bit can return -ENOMEM, which is most of the
+ * time a temporary error. So when it happens, ignore the error
+ * and wait for writeback of this range to finish - because we
+ * failed to set the bit EXTENT_NEED_WAIT for the range, a call
+ * to btrfs_wait_marked_extents() would not know that writeback
+ * for this range started and therefore wouldn't wait for it to
+ * finish - we don't want to commit a superblock that points to
+ * btree nodes/leafs for which writeback hasn't finished yet
+ * (and without errors).
+ * We cleanup any entries left in the io tree when committing
+ * the transaction (through clear_btree_io_tree()).
+ */
+ if (err == -ENOMEM) {
+ err = 0;
+ wait_writeback = true;
+ }
+ if (!err)
+ err = filemap_fdatawrite_range(mapping, start, end);
if (err)
werr = err;
+ else if (wait_writeback)
+ werr = filemap_fdatawait_range(mapping, start, end);
+ cached_state = NULL;
cond_resched();
start = end + 1;
}
- if (err)
- werr = err;
return werr;
}
@@ -862,9 +910,21 @@
while (!find_first_extent_bit(dirty_pages, start, &start, &end,
EXTENT_NEED_WAIT, &cached_state)) {
- clear_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
- 0, 0, &cached_state, GFP_NOFS);
- err = filemap_fdatawait_range(mapping, start, end);
+ /*
+ * Ignore -ENOMEM errors returned by clear_extent_bit().
+ * When committing the transaction, we'll remove any entries
+ * left in the io tree. For a log commit, we don't remove them
+ * after committing the log because the tree can be accessed
+ * concurrently - we do it only at transaction commit time when
+ * it's safe to do it (through clear_btree_io_tree()).
+ */
+ err = clear_extent_bit(dirty_pages, start, end,
+ EXTENT_NEED_WAIT,
+ 0, 0, &cached_state, GFP_NOFS);
+ if (err == -ENOMEM)
+ err = 0;
+ if (!err)
+ err = filemap_fdatawait_range(mapping, start, end);
if (err)
werr = err;
cond_resched();
@@ -919,17 +979,17 @@
return 0;
}
-int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
+static int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
struct btrfs_root *root)
{
- if (!trans || !trans->transaction) {
- struct inode *btree_inode;
- btree_inode = root->fs_info->btree_inode;
- return filemap_write_and_wait(btree_inode->i_mapping);
- }
- return btrfs_write_and_wait_marked_extents(root,
+ int ret;
+
+ ret = btrfs_write_and_wait_marked_extents(root,
&trans->transaction->dirty_pages,
EXTENT_DIRTY);
+ clear_btree_io_tree(&trans->transaction->dirty_pages);
+
+ return ret;
}
/*