[PATCH 3.2 058/221] debugfs: leave freeing a symlink body until inode eviction

Ben Hutchings
2015-05-05T01:44:49Z

From: Al Viro <viro@zeniv.linux.org.uk>

commit 0db59e59299f0b67450c5db21f7f316c8fb04e84 upstream.

As it is, we have debugfs_remove() racing with symlink traversals.
Supply ->evict_inode() and do freeing there - inode will remain
pinned until we are done with the symlink body.

And rip the idiocy with checking if dentry is positive right after
we'd verified debugfs_positive(), which is a stronger check...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[bwh: Backported to 3.2:
- Plumb in debugfs_super_operations, which we didn't previously define
- Call truncate_inode_pages() instead of truncate_inode_pages_final()
- Call end_writeback() instead of clear_inode()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -125,11 +125,30 @@ static inline int debugfs_positive(struc
return dentry->d_inode && !d_unhashed(dentry);
}

+static void debugfs_evict_inode(struct inode *inode)
+{
+ truncate_inode_pages(&inode->i_data, 0);
+ end_writeback(inode);
+ if (S_ISLNK(inode->i_mode))
+ kfree(inode->i_private);
+}
+
+static const struct super_operations debugfs_super_operations = {
+ .evict_inode = debugfs_evict_inode,
+};
+
static int debug_fill_super(struct super_block *sb, void *data, int silent)
{
static struct tree_descr debug_files[] = {{""}};
+ int err;
+
+ err = simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
+ if (err)
+ return err;

- return simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
+ sb->s_op = &debugfs_super_operations;
+
+ return 0;
}

static struct dentry *debug_mount(struct file_system_type *fs_type,
@@ -312,23 +331,14 @@ static int __debugfs_remove(struct dentr
int ret = 0;

if (debugfs_positive(dentry)) {
- if (dentry->d_inode) {
- dget(dentry);
- switch (dentry->d_inode->i_mode & S_IFMT) {
- case S_IFDIR:
- ret = simple_rmdir(parent->d_inode, dentry);
- break;
- case S_IFLNK:
- kfree(dentry->d_inode->i_private);
- /* fall through */
- default:
- simple_unlink(parent->d_inode, dentry);
- break;
- }
- if (!ret)
- d_delete(dentry);
- dput(dentry);
- }
+ dget(dentry);
+ if (S_ISDIR(dentry->d_inode->i_mode))
+ ret = simple_rmdir(parent->d_inode, dentry);
+ else
+ simple_unlink(parent->d_inode, dentry);
+ if (!ret)
+ d_delete(dentry);
+ dput(dentry);
}
return ret;
}