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Commit 3f8a18cc authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
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Btrfs: hold the commit_root_sem when getting the commit root during send 



We currently rely too heavily on roots being read-only to save us from just
accessing root->commit_root.  We can easily balance blocks out from underneath a
read only root, so to save us from getting screwed make sure we only access
root->commit_root under the commit root sem.  Thanks,

Signed-off-by: default avatarJosef Bacik <jbacik@fb.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
parent 9e351cc8

fs/btrfs/ctree.c

+6 −0
Original line number Diff line number Diff line
@@ -2769,9 +2769,13 @@ again: 
		 * the commit roots are read only

		 * so we always do read locks

		 */

		if (p->need_commit_sem)

			down_read(&root->fs_info->commit_root_sem);

		b = root->commit_root;

		extent_buffer_get(b);

		level = btrfs_header_level(b);

		if (p->need_commit_sem)

			up_read(&root->fs_info->commit_root_sem);

		if (!p->skip_locking)

			btrfs_tree_read_lock(b);

	} else {
@@ -5436,6 +5440,7 @@ int btrfs_compare_trees(struct btrfs_root *left_root, 
	 *   the right if possible or go up and right.

	 */



	down_read(&left_root->fs_info->commit_root_sem);

	left_level = btrfs_header_level(left_root->commit_root);

	left_root_level = left_level;

	left_path->nodes[left_level] = left_root->commit_root;
@@ -5445,6 +5450,7 @@ int btrfs_compare_trees(struct btrfs_root *left_root, 
	right_root_level = right_level;

	right_path->nodes[right_level] = right_root->commit_root;

	extent_buffer_get(right_path->nodes[right_level]);

	up_read(&left_root->fs_info->commit_root_sem);



	if (left_level == 0)

		btrfs_item_key_to_cpu(left_path->nodes[left_level],

fs/btrfs/ctree.h

+1 −0
Original line number Diff line number Diff line
@@ -609,6 +609,7 @@ struct btrfs_path { 
	unsigned int skip_locking:1;

	unsigned int leave_spinning:1;

	unsigned int search_commit_root:1;

	unsigned int need_commit_sem:1;

};



/*

fs/btrfs/send.c

+32 −16
Original line number Diff line number Diff line
@@ -493,6 +493,7 @@ static struct btrfs_path *alloc_path_for_send(void) 
		return NULL;

	path->search_commit_root = 1;

	path->skip_locking = 1;

	path->need_commit_sem = 1;

	return path;

}
@@ -771,29 +772,22 @@ out: 
/*

 * Helper function to retrieve some fields from an inode item.

 */

static int get_inode_info(struct btrfs_root *root,

			  u64 ino, u64 *size, u64 *gen,

			  u64 *mode, u64 *uid, u64 *gid,

			  u64 *rdev)

static int __get_inode_info(struct btrfs_root *root, struct btrfs_path *path,

			  u64 ino, u64 *size, u64 *gen, u64 *mode, u64 *uid,

			  u64 *gid, u64 *rdev)

{

	int ret;

	struct btrfs_inode_item *ii;

	struct btrfs_key key;

	struct btrfs_path *path;



	path = alloc_path_for_send();

	if (!path)

		return -ENOMEM;



	key.objectid = ino;

	key.type = BTRFS_INODE_ITEM_KEY;

	key.offset = 0;

	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);

	if (ret < 0)

		goto out;

	if (ret) {

		if (ret > 0)

			ret = -ENOENT;

		goto out;

		return ret;

	}



	ii = btrfs_item_ptr(path->nodes[0], path->slots[0],
@@ -811,7 +805,22 @@ static int get_inode_info(struct btrfs_root *root, 
	if (rdev)

		*rdev = btrfs_inode_rdev(path->nodes[0], ii);



out:

	return ret;

}



static int get_inode_info(struct btrfs_root *root,

			  u64 ino, u64 *size, u64 *gen,

			  u64 *mode, u64 *uid, u64 *gid,

			  u64 *rdev)

{

	struct btrfs_path *path;

	int ret;



	path = alloc_path_for_send();

	if (!path)

		return -ENOMEM;

	ret = __get_inode_info(root, path, ino, size, gen, mode, uid, gid,

			       rdev);

	btrfs_free_path(path);

	return ret;

}
@@ -1085,6 +1094,7 @@ out: 
struct backref_ctx {

	struct send_ctx *sctx;



	struct btrfs_path *path;

	/* number of total found references */

	u64 found;
@@ -1155,8 +1165,9 @@ static int __iterate_backrefs(u64 ino, u64 offset, u64 root, void *ctx_) 
	 * There are inodes that have extents that lie behind its i_size. Don't

	 * accept clones from these extents.

	 */

	ret = get_inode_info(found->root, ino, &i_size, NULL, NULL, NULL, NULL,

			NULL);

	ret = __get_inode_info(found->root, bctx->path, ino, &i_size, NULL, NULL,

			       NULL, NULL, NULL);

	btrfs_release_path(bctx->path);

	if (ret < 0)

		return ret;
@@ -1235,12 +1246,17 @@ static int find_extent_clone(struct send_ctx *sctx, 
	if (!tmp_path)

		return -ENOMEM;



	/* We only use this path under the commit sem */

	tmp_path->need_commit_sem = 0;



	backref_ctx = kmalloc(sizeof(*backref_ctx), GFP_NOFS);

	if (!backref_ctx) {

		ret = -ENOMEM;

		goto out;

	}



	backref_ctx->path = tmp_path;



	if (data_offset >= ino_size) {

		/*

		 * There may be extents that lie behind the file's size.