[RFC] a couple of i_nlink fixes in btrfs

[RFC] a couple of i_nlink fixes in btrfs

[Al Viro]

	a) rename() plays with i_nlink of old_inode; bad, since it's not
locked.  I'd add a variant of btrfs_unlink_inode() that would leave
btrfs_drop_nlink()/btrfs_update_inode() to callers and use it instead.
	b) btrfs_link() doesn't check for i_nlink overflows.  I don't
know if there's anything preventing that many links to a file on btrfs,
but if there is, it's at least worth a comment in there...

	Please, review; patches in followups or in #btrfs in vfs-2.6.git

[PATCH 1/2] btrfs: don't mess with i_nlink of unlocked inode in rename()

[Al Viro]

old_inode is not locked; it's not safe to play with its link
count.  Instead of bumping it and calling btrfs_unlink_inode(),
add a variant of the latter that does not do btrfs_drop_nlink()/
btrfs_update_inode(), call it instead of btrfs_inc_nlink()/
btrfs_unlink_inode() and do btrfs_update_inode() ourselves.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/btrfs/inode.c |   36 +++++++++++++++++++++++++-----------
 1 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 0efdb65..099d64c 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2634,10 +2634,10 @@ failed:
  * recovery code.  It remove a link in a directory with a given name, and
  * also drops the back refs in the inode to the directory
  */
-int btrfs_unlink_inode(struct btrfs_trans_handle *trans,
-		       struct btrfs_root *root,
-		       struct inode *dir, struct inode *inode,
-		       const char *name, int name_len)
+static int __btrfs_unlink_inode(struct btrfs_trans_handle *trans,
+				struct btrfs_root *root,
+				struct inode *dir, struct inode *inode,
+				const char *name, int name_len)
 {
 	struct btrfs_path *path;
 	int ret = 0;
@@ -2709,12 +2709,25 @@ err:
 	btrfs_i_size_write(dir, dir->i_size - name_len * 2);
 	inode->i_ctime = dir->i_mtime = dir->i_ctime = CURRENT_TIME;
 	btrfs_update_inode(trans, root, dir);
-	btrfs_drop_nlink(inode);
-	ret = btrfs_update_inode(trans, root, inode);
 out:
 	return ret;
 }
 
+int btrfs_unlink_inode(struct btrfs_trans_handle *trans,
+		       struct btrfs_root *root,
+		       struct inode *dir, struct inode *inode,
+		       const char *name, int name_len)
+{
+	int ret;
+	ret = __btrfs_unlink_inode(trans, root, dir, inode, name, name_len);
+	if (!ret) {
+		btrfs_drop_nlink(inode);
+		ret = btrfs_update_inode(trans, root, inode);
+	}
+	return ret;
+}
+		
+
 /* helper to check if there is any shared block in the path */
 static int check_path_shared(struct btrfs_root *root,
 			     struct btrfs_path *path)
@@ -6908,11 +6921,12 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 					old_dentry->d_name.name,
 					old_dentry->d_name.len);
 	} else {
-		btrfs_inc_nlink(old_dentry->d_inode);
-		ret = btrfs_unlink_inode(trans, root, old_dir,
-					 old_dentry->d_inode,
-					 old_dentry->d_name.name,
-					 old_dentry->d_name.len);
+		ret = __btrfs_unlink_inode(trans, root, old_dir,
+					old_dentry->d_inode,
+					old_dentry->d_name.name,
+					old_dentry->d_name.len);
+		if (!ret)
+			ret = btrfs_update_inode(trans, root, old_inode);
 	}
 	BUG_ON(ret);
 
-- 
1.7.2.5

[PATCH 2/2] btrfs: check link counter overflow in link(2)

[Al Viro]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/btrfs/inode.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 099d64c..8a6df03 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4826,6 +4826,9 @@ static int btrfs_link(struct dentry *old_dentry, struct inode *dir,
 	if (root->objectid != BTRFS_I(inode)->root->objectid)
 		return -EPERM;
 
+	if (inode->i_nlink == ~0U)
+		return -EMLINK;
+
 	btrfs_inc_nlink(inode);
 	inode->i_ctime = CURRENT_TIME;
 
-- 
1.7.2.5

Re: [RFC] a couple of i_nlink fixes in btrfs

[Chris Mason]

Excerpts from Al Viro's message of 2011-03-04 12:13:53 -0500:
>     a) rename() plays with i_nlink of old_inode; bad, since it's not
> locked.  I'd add a variant of btrfs_unlink_inode() that would leave
> btrfs_drop_nlink()/btrfs_update_inode() to callers and use it instead.
>     b) btrfs_link() doesn't check for i_nlink overflows.  I don't
> know if there's anything preventing that many links to a file on btrfs,
> but if there is, it's at least worth a comment in there...
> 
>     Please, review; patches in followups or in #btrfs in vfs-2.6.git

Thanks, these both look good but I'll test here as well.  Are you
planning on pushing for .38?

-chris

Re: [RFC] a couple of i_nlink fixes in btrfs

[Al Viro]

On Mon, Mar 07, 2011 at 11:58:13AM -0500, Chris Mason wrote:

> Thanks, these both look good but I'll test here as well.  Are you
> planning on pushing for .38?

No, but .39 would be nice ;-)  Do you want that to go through btrfs tree
or through vfs one?

Re: [RFC] a couple of i_nlink fixes in btrfs

[Chris Mason]

Excerpts from Al Viro's message of 2011-03-21 01:17:25 -0400:
> On Mon, Mar 07, 2011 at 11:58:13AM -0500, Chris Mason wrote:
> 
> > Thanks, these both look good but I'll test here as well.  Are you
> > planning on pushing for .38?
> 
> No, but .39 would be nice ;-)  Do you want that to go through btrfs tree
> or through vfs one?

I'll take them in mine, it'll be easier to put in with all these other
changes.

-chris