Btrfs: fix freeing delayed ref head while still holding its mutex (eb12db69) · Commits · 戴 / test

I hit this error when reproducing a bug that would end in a transaction abort. We take the delayed ref head's mutex to keep anybody from processing it while we're destroying it, but we fail to drop the mutex before we carry on and free the damned thing. Fix this by doing the remove logic for the head ourselves and unlock the mutex, that way we can avoid use after free's or hung tasks waiting on that mutex to come back so they know the delayed ref completed. Thanks, Signed-off-by:

Josef Bacik <jbacik@fusionio.com>

fs/btrfs/disk-io.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -3615,11 +3615,11 @@ int btrfs_destroy_delayed_refs(struct btrfs_transaction *trans,
		}

		while ((node = rb_first(&delayed_refs->root)) != NULL) {
		ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
		struct btrfs_delayed_ref_head *head = NULL;

		ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
		atomic_set(&ref->refs, 1);
		if (btrfs_delayed_ref_is_head(ref)) {
		struct btrfs_delayed_ref_head *head;

		head = btrfs_delayed_node_to_head(ref);
		if (!mutex_trylock(&head->mutex)) {
		@@ -3641,10 +3641,12 @@ int btrfs_destroy_delayed_refs(struct btrfs_transaction *trans,
		delayed_refs->num_heads_ready--;
		list_del_init(&head->cluster);
		}

		ref->in_tree = 0;
		rb_erase(&ref->rb_node, &delayed_refs->root);
		delayed_refs->num_entries--;

		if (head)
		mutex_unlock(&head->mutex);
		spin_unlock(&delayed_refs->lock);
		btrfs_put_delayed_ref(ref);

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