Josef Bacik
2014-Mar-28 21:16 UTC
[PATCH] 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: 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(+)
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;
}
--
1.8.3.1
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