[Devel] [PATCH RHEL7 COMMIT] ms/ext4: work around deleting a file with i_nlink == 0 safely

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1127.8.2.vz7.151.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.8.2.vz7.151.8
------>
commit 4b378ce020980ad32590b8595ac43f53b43c7ea5
Author: Vasily Averin <vvs at virtuozzo.com>
Date:   Fri May 29 19:47:15 2020 +0300

    ms/ext4: work around deleting a file with i_nlink == 0 safely
    
    ML commit c7df4a1ecb8579838ec8c56b2bb6a6716e974f37
    Author: Theodore Ts'o <tytso at mit.edu>
    Date:   Mon Nov 11 22:18:13 2019 -0500
    
        ext4: work around deleting a file with i_nlink == 0 safely
    
        If the file system is corrupted such that a file's i_links_count is
        too small, then it's possible that when unlinking that file, i_nlink
        will already be zero.  Previously we were working around this kind of
        corruption by forcing i_nlink to one; but we were doing this before
        trying to delete the directory entry --- and if the file system is
        corrupted enough that ext4_delete_entry() fails, then we exit with
        i_nlink elevated, and this causes the orphan inode list handling to be
        FUBAR'ed, such that when we unmount the file system, the orphan inode
        list can get corrupted.
    
        A better way to fix this is to simply skip trying to call drop_nlink()
        if i_nlink is already zero, thus moving the check to the place where
        it makes the most sense.
    
        https://bugzilla.kernel.org/show_bug.cgi?id=205433
    
        Link: https://lore.kernel.org/r/20191112032903.8828-1-tytso@mit.edu
        Signed-off-by: Theodore Ts'o <tytso at mit.edu>
        Cc: stable at kernel.org
        Reviewed-by: Andreas Dilger <adilger at dilger.ca>
    
    [vvs@] taken from RHEl7.9 beta kernel
    2020-03-11 Jan Stancek <jstancek at redhat.com> [3.10.0-1128.el7]
        - [fs] ext4: work around deleting a file with i_nlink == 0 safely (Carlos Maiolino) [1801046]
    
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 fs/ext4/namei.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 24d8617685b1d..c8c56ef9281d0 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2846,19 +2846,18 @@ static int ext4_unlink(struct inode *dir, struct dentry *dentry)
 	if (inode == EXT4_SB(dir->i_sb)->s_balloon_ino)
 		goto end_unlink;
 
-	if (!inode->i_nlink) {
-		ext4_warning(inode->i_sb,
-			     "Deleting nonexistent file (%lu), %d",
-			     inode->i_ino, inode->i_nlink);
-		set_nlink(inode, 1);
-	}
 	retval = ext4_delete_entry(handle, dir, de, bh);
 	if (retval)
 		goto end_unlink;
 	dir->i_ctime = dir->i_mtime = ext4_current_time(dir);
 	ext4_update_dx_flag(dir);
 	ext4_mark_inode_dirty(handle, dir);
-	drop_nlink(inode);
+	if (inode->i_nlink == 0)
+		ext4_warning(inode->i_sb,
+			     "Deleting nonexistent file (%lu), %d",
+			     inode->i_ino, inode->i_nlink);
+	else
+		drop_nlink(inode);
 	if (!inode->i_nlink)
 		ext4_orphan_add(handle, inode);
 	inode->i_ctime = ext4_current_time(inode);