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xfs: reset child dir '..' entry when unlinking child

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While running xfs/168, I noticed a second source of post-shrink
corruption errors causing shutdowns.

Let's say that directory B has a low inode number and is a child of
directory A, which has a high number.  If B is empty but open, and
unlinked from A, B's dotdot link continues to point to A.  If A is then
unlinked and the filesystem shrunk so that A is no longer a valid inode,
a subsequent AIL push of B will trip the inode verifiers because the
dotdot entry points outside of the filesystem.

To avoid this problem, reset B's dotdot entry to the root directory when
unlinking directories, since the root directory cannot be removed.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
This commit is contained in:
Darrick J. Wong 2021-07-12 12:58:48 -07:00
parent da062d16a8
commit 5838d0356b
1 changed files with 13 additions and 0 deletions
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13
fs/xfs/xfs_inode.c
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@ -2763,6 +2763,19 @@ xfs_remove(
error = xfs_droplink(tp, ip);
if (error)
goto out_trans_cancel;
/*
* Point the unlinked child directory's ".." entry to the root
* directory to eliminate back-references to inodes that may
* get freed before the child directory is closed. If the fs
* gets shrunk, this can lead to dirent inode validation errors.
*/
if (dp->i_ino != tp->t_mountp->m_sb.sb_rootino) {
error = xfs_dir_replace(tp, ip, &xfs_name_dotdot,
tp->t_mountp->m_sb.sb_rootino, 0);
if (error)
return error;
}
} else {
/*
* When removing a non-directory we need to log the parent