From: Zheng Liu <wenqing.lz@xxxxxxxxxx>
This patch makes overlayfs count subdirs to get the correct link count
because 9pfs needs this. Otherwise, we will get a warning message from
inc_nlink() because inode->i_nlink == 0 and inode->i_state w/o
I_LINKABLE flag in a virtualization environment. The warning message
looks like as below.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 27343 at ../fs/inode.c:330 inc_nlink+0x32/0x50()
Modules linked in:
CPU: 0 PID: 27343 Comm: mkdir Tainted: G W 4.1.6+ #1
ffffffff81540a0e ffff88046b103da8 ffffffff8120d849 ffff88046b103db8
ffffffff8120d897 ffff88046b103df8 ffffffff81044bbd ffff88046b2a0403
ffff88046b936d68 0000000000000000 ffff88046b936d68 ffff88046b2a9300
Call Trace:
[<ffffffff8120d849>] __dump_stack+0x19/0x20
[<ffffffff8120d897>] dump_stack+0x47/0x60
[<ffffffff81044bbd>] warn_slowpath_common+0xad/0xe0
[<ffffffff81044c0a>] warn_slowpath_null+0x1a/0x20
[<ffffffff8117caa2>] inc_nlink+0x32/0x50
[<ffffffff811d3c89>] v9fs_vfs_mkdir_dotl+0x269/0x2b0
[<ffffffff8116f9a9>] vfs_mkdir+0x89/0xd0
[<ffffffff81173912>] SyS_mkdirat+0x82/0xd0
[<ffffffff8116dae9>] SyS_mkdir+0x19/0x20
[<ffffffff813b29d7>] system_call_fastpath+0x12/0x6a
---[ end trace dd0930847ec4e6d2 ]---
The root cause is that overlayfs doesn't count subdirs and it reports
a wrong link count. From the output of stat(1) we can seen that the
'Links' of a directory is 1, but at least it should be 2. When creating
a directory in 9pfs, the parent directory's inode->i_nlink is 0 and a
WARN_ON will be triggered.
This warning can be reproduced by the following steps.
[In host os]
1. build a ROOTFS for booting up a vm using 9pfs
2. mount -t overlay -olowerdir=${lower},upperdir=${upper},workdir={work} none ${ROOTFS}/mnt
3. run a vm using 9pfs
e.g. http://www.linux-kvm.org/page/9p_virtio
[In guest os]
4. cd /mnt
5. mkdir 1
6. rm -rf 1; mkdir 1
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Signed-off-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
---
fs/overlayfs/dir.c | 8 --------
1 file changed, 8 deletions(-)
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 692ceda..fbeb841 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -147,14 +147,6 @@ static int ovl_dir_getattr(struct vfsmount *mnt, struct dentry *dentry,
stat->dev = dentry->d_sb->s_dev;
stat->ino = dentry->d_inode->i_ino;
- /*
- * It's probably not worth it to count subdirs to get the
- * correct link count. nlink=1 seems to pacify 'find' and
- * other utilities.
- */
- if (OVL_TYPE_MERGE(type))
- stat->nlink = 1;
-
return 0;
}
--
2.4.0.rc3.3.g6eb1401
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