[PATCH 3.4 046/172] debugfs: leave freeing a symlink body until inode eviction

[lizf]

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

3.4.108-rc1 review patch.  If anyone has any objections, please let me know.

------------------


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@xxxxxxxxxxxxxxxxxx>
[lizf: Backported to 3.4:
 - call end_writeback() instead of clear_inode()
 - call truncate_inode_pages() instead of truncate_inode_pages_final()]
Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>
---
 fs/debugfs/inode.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 47d64e9..7b65755 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -238,10 +238,19 @@ static int debugfs_show_options(struct seq_file *m, struct dentry *root)
 	return 0;
 }
 
+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 = {
 	.statfs		= simple_statfs,
 	.remount_fs	= debugfs_remount,
 	.show_options	= debugfs_show_options,
+	.evict_inode	= debugfs_evict_inode,
 };
 
 static int debug_fill_super(struct super_block *sb, void *data, int silent)
@@ -459,23 +468,14 @@ static int __debugfs_remove(struct dentry *dentry, struct dentry *parent)
 	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;
 }
-- 
1.9.1

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