Btrfs: hold the commit_root_sem when getting the commit root during send
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Message ID 1396041361-7082-1-git-send-email-jbacik@fb.com
State Accepted
Headers show

Commit Message

Josef Bacik March 28, 2014, 9:16 p.m. UTC
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: Josef Bacik <jbacik@fb.com>
---
 fs/btrfs/ctree.c | 6 ++++++
 fs/btrfs/ctree.h | 1 +
 fs/btrfs/send.c  | 1 +
 3 files changed, 8 insertions(+)

Patch
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diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 71bbafe..0e9569c 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -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],
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2277006..453d859 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -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;
 };
 
 /*
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 6f035ee..7e7552c 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -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;
 }