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ovl: fix WARN_ON nlink drop to zero

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Changes to underlying layers should not cause WARN_ON(), but this repro
does:

 mkdir w l u mnt
 sudo mount -t overlay -o workdir=w,lowerdir=l,upperdir=u overlay mnt
 touch mnt/h
 ln u/h u/k
 rm -rf mnt/k
 rm -rf mnt/h
 dmesg

 ------------[ cut here ]------------
 WARNING: CPU: 1 PID: 116244 at fs/inode.c:302 drop_nlink+0x28/0x40

After upper hardlinks were added while overlay is mounted, unlinking all
overlay hardlinks drops overlay nlink to zero before all upper inodes
are unlinked.

After unlink/rename prevent i_nlink from going to zero if there are still
hashed aliases (i.e. cached hard links to the victim) remaining.

Reported-by: Phasip <phasip@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi 2020-03-27 16:51:02 +01:00
parent a5a84682ec
commit 83552eacdf
1 changed files with 24 additions and 2 deletions
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26
fs/overlayfs/dir.c
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@ -822,6 +822,28 @@ static bool ovl_pure_upper(struct dentry *dentry)
!ovl_test_flag(OVL_WHITEOUTS, d_inode(dentry));
}
static void ovl_drop_nlink(struct dentry *dentry)
{
struct inode *inode = d_inode(dentry);
struct dentry *alias;
/* Try to find another, hashed alias */
spin_lock(&inode->i_lock);
hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
if (alias != dentry && !d_unhashed(alias))
break;
}
spin_unlock(&inode->i_lock);
/*
* Changes to underlying layers may cause i_nlink to lose sync with
* reality. In this case prevent the link count from going to zero
* prematurely.
*/
if (inode->i_nlink > !!alias)
drop_nlink(inode);
}
static int ovl_do_remove(struct dentry *dentry, bool is_dir)
{
int err;
@ -859,7 +881,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
if (is_dir)
clear_nlink(dentry->d_inode);
else
drop_nlink(dentry->d_inode);
ovl_drop_nlink(dentry);
}
ovl_nlink_end(dentry);
@ -1204,7 +1226,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *old,
if (new_is_dir)
clear_nlink(d_inode(new));
else
drop_nlink(d_inode(new));
ovl_drop_nlink(new);
}
ovl_dir_modified(old->d_parent, ovl_type_origin(old) ||