Re: [PATCH] ovl: fix some bug exist in ovl_get_inode

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, May 27, 2020 at 02:16:00PM +0300, Amir Goldstein wrote:
> On Wed, May 27, 2020 at 6:45 AM yangerkun <yangerkun@huawei.com> wrote:
> >
> > Run generic/461 with ext4 upper/lower layer sometimes may trigger the
> > bug as below(linux 4.19):
> >
> > [  551.001349] overlayfs: failed to get metacopy (-5)
> > [  551.003464] overlayfs: failed to get inode (-5)
> > [  551.004243] overlayfs: cleanup of 'd44/fd51' failed (-5)
> > [  551.004941] overlayfs: failed to get origin (-5)
> > [  551.005199] ------------[ cut here ]------------
> > [  551.006697] WARNING: CPU: 3 PID: 24674 at fs/inode.c:1528 iput+0x33b/0x400
> > ...
> > [  551.027219] Call Trace:
> > [  551.027623]  ovl_create_object+0x13f/0x170
> > [  551.028268]  ovl_create+0x27/0x30
> > [  551.028799]  path_openat+0x1a35/0x1ea0
> > [  551.029377]  do_filp_open+0xad/0x160
> > [  551.029944]  ? vfs_writev+0xe9/0x170
> > [  551.030499]  ? page_counter_try_charge+0x77/0x120
> > [  551.031245]  ? __alloc_fd+0x160/0x2a0
> > [  551.031832]  ? do_sys_open+0x189/0x340
> > [  551.032417]  ? get_unused_fd_flags+0x34/0x40
> > [  551.033081]  do_sys_open+0x189/0x340
> > [  551.033632]  __x64_sys_creat+0x24/0x30
> > [  551.034219]  do_syscall_64+0xd5/0x430
> > [  551.034800]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > ...
> > [  556.107515] BUG: Dentry 000000006bc1d73f{i=4129c,n=fd51}  still in use (-1) [unmount of ext4 sdb]
> > [  556.108946] ------------[ cut here ]------------
> > [  556.109686] WARNING: CPU: 1 PID: 24682 at fs/dcache.c:1557 umount_check+0x95/0xc0
> > [  556.130343]  d_walk+0x10d/0x430
> > [  556.130832]  do_one_tree+0x30/0x60
> > [  556.131365]  shrink_dcache_for_umount+0x38/0xe0
> > [  556.132063]  generic_shutdown_super+0x2e/0x1c0
> > [  556.132747]  kill_block_super+0x29/0x80
> > [  556.133338]  deactivate_locked_super+0x7a/0x100
> > [  556.134034]  deactivate_super+0x9d/0xb0
> > [  556.134627]  cleanup_mnt+0x67/0x100
> > [  556.135173]  __cleanup_mnt+0x16/0x20
> > [  556.135731]  task_work_run+0xdb/0x110
> > [  556.136306]  exit_to_usermode_loop+0x197/0x1b0
> > [  556.136991]  do_syscall_64+0x3ce/0x430
> > [  556.137571]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > ...
> > [  556.378140] VFS: Busy inodes after unmount of sdb. Self-destruct in 5 seconds.  Have a nice day...
> >
> > After check the code, there may some bug need to fix:
> > 1. We need to call iput once ovl_check_metacopy_xattr fail.
> > 2. We need to call unlock_new_inode or the above iput(also with iput in
> >    ovl_create_object) will trigger the a WARN_ON since  the I_NEW still
> >    exists.
> > 3. We should move the init for upperdentry to the place below
> >    ovl_check_metacopy_xattr. Or the dentry reference will decrease to
> >    -1(error path in ovl_create_upper will inc, ovl_destroy_inode too).
> >
> 
> OR we don't check metacopy xattr in ovl_get_inode().
> 
> In ovl_lookup() we already checked metacopy xattr.
> No reason to check it again in this subtle context.
> 
> In ovl_lookup() can store value of upper metacopy and after we get
> the inode, set the OVL_UPPERDATA inode flag according to
> upperdentry && !uppermetacopy.
> 
> That would be consistent with ovl_obtain_alias() which sets the
> OVL_UPPERDATA inode flag after getting the inode.

Hi Amir,

This patch implements what you are suggesting. Compile tested only.
Does this look ok?

May be I don't need to split it up in lmetacopy and umetacopy. Ideally,
lookup in lower layers should stop if an upper regular file is not
metacopy. IOW, (upperdentry && !metacopy) might be sufficient check.
Will look closely if this patch looks fine.

Thanks
Vivek


---
 fs/overlayfs/inode.c |   11 +----------
 fs/overlayfs/namei.c |   12 +++++++-----
 2 files changed, 8 insertions(+), 15 deletions(-)

Index: redhat-linux/fs/overlayfs/namei.c
===================================================================
--- redhat-linux.orig/fs/overlayfs/namei.c	2020-04-13 13:52:53.438294244 -0400
+++ redhat-linux/fs/overlayfs/namei.c	2020-05-27 15:28:38.242809626 -0400
@@ -823,7 +823,7 @@ struct dentry *ovl_lookup(struct inode *
 	struct dentry *this;
 	unsigned int i;
 	int err;
-	bool metacopy = false;
+	bool lmetacopy = false, umetacopy=false;
 	struct ovl_lookup_data d = {
 		.sb = dentry->d_sb,
 		.name = dentry->d_name,
@@ -869,7 +869,7 @@ struct dentry *ovl_lookup(struct inode *
 				goto out_put_upper;
 
 			if (d.metacopy)
-				metacopy = true;
+				umetacopy = true;
 		}
 
 		if (d.redirect) {
@@ -941,7 +941,7 @@ struct dentry *ovl_lookup(struct inode *
 		}
 
 		if (d.metacopy)
-			metacopy = true;
+			lmetacopy = true;
 		/*
 		 * Do not store intermediate metacopy dentries in chain,
 		 * except top most lower metacopy dentry
@@ -982,7 +982,7 @@ struct dentry *ovl_lookup(struct inode *
 		}
 	}
 
-	if (metacopy) {
+	if (lmetacopy || umetacopy) {
 		/*
 		 * Found a metacopy dentry but did not find corresponding
 		 * data dentry
@@ -1023,7 +1023,7 @@ struct dentry *ovl_lookup(struct inode *
 	 *
 	 * Always lookup index of non-dir non-metacopy and non-upper.
 	 */
-	if (ctr && (!upperdentry || (!d.is_dir && !metacopy)))
+	if (ctr && (!upperdentry || (!d.is_dir && !(lmetacopy || umetacopy))))
 		origin = stack[0].dentry;
 
 	if (origin && ovl_indexdir(dentry->d_sb) &&
@@ -1074,6 +1074,8 @@ struct dentry *ovl_lookup(struct inode *
 		err = PTR_ERR(inode);
 		if (IS_ERR(inode))
 			goto out_free_oe;
+		if (upperdentry && !umetacopy)
+			ovl_set_flag(OVL_UPPERDATA, inode);
 	}
 
 	ovl_dentry_update_reval(dentry, upperdentry,
Index: redhat-linux/fs/overlayfs/inode.c
===================================================================
--- redhat-linux.orig/fs/overlayfs/inode.c	2020-04-22 11:32:28.237700957 -0400
+++ redhat-linux/fs/overlayfs/inode.c	2020-05-27 15:30:21.059809626 -0400
@@ -939,7 +939,7 @@ struct inode *ovl_get_inode(struct super
 	bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry,
 					oip->index);
 	int fsid = bylower ? lowerpath->layer->fsid : 0;
-	bool is_dir, metacopy = false;
+	bool is_dir;
 	unsigned long ino = 0;
 	int err = oip->newinode ? -EEXIST : -ENOMEM;
 
@@ -1000,15 +1000,6 @@ struct inode *ovl_get_inode(struct super
 	if (oip->index)
 		ovl_set_flag(OVL_INDEX, inode);
 
-	if (upperdentry) {
-		err = ovl_check_metacopy_xattr(upperdentry);
-		if (err < 0)
-			goto out_err;
-		metacopy = err;
-		if (!metacopy)
-			ovl_set_flag(OVL_UPPERDATA, inode);
-	}
-
 	OVL_I(inode)->redirect = oip->redirect;
 
 	if (bylower)