linux-kernel - [PATCH 4.0 111/220] mnt: Delay removal from the mount hash.

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Message-Id: <20150502185859.122617350@linuxfoundation.org>
Date:	Sat,  2 May 2015 21:00:26 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 4.0 111/220] mnt: Delay removal from the mount hash.

4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@...ssion.com>

commit 411a938b5abc9cb126c41cccf5975ae464fe0f3e upstream.

- Modify __lookup_mnt_hash_last to ignore mounts that have MNT_UMOUNTED set.
- Don't remove mounts from the mount hash table in propogate_umount
- Don't remove mounts from the mount hash table in umount_tree before
  the entire list of mounts to be umounted is selected.
- Remove mounts from the mount hash table as the last thing that
  happens in the case where a mount has a parent in umount_tree.
  Mounts without parents are not hashed (by definition).

This paves the way for delaying removal from the mount hash table even
farther and fixing the MNT_LOCKED vs MNT_DETACH issue.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/namespace.c |   13 ++++++++-----
 fs/pnode.c     |    1 -
 2 files changed, 8 insertions(+), 6 deletions(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -632,14 +632,17 @@ struct mount *__lookup_mnt(struct vfsmou
  */
 struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
 {
-	struct mount *p, *res;
-	res = p = __lookup_mnt(mnt, dentry);
+	struct mount *p, *res = NULL;
+	p = __lookup_mnt(mnt, dentry);
 	if (!p)
 		goto out;
+	if (!(p->mnt.mnt_flags & MNT_UMOUNT))
+		res = p;
 	hlist_for_each_entry_continue(p, mnt_hash) {
 		if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry)
 			break;
-		res = p;
+		if (!(p->mnt.mnt_flags & MNT_UMOUNT))
+			res = p;
 	}
 out:
 	return res;
@@ -1338,9 +1341,8 @@ static void umount_tree(struct mount *mn
 		list_move(&p->mnt_list, &tmp_list);
 	}
 
-	/* Hide the mounts from lookup_mnt and mnt_mounts */
+	/* Hide the mounts from mnt_mounts */
 	list_for_each_entry(p, &tmp_list, mnt_list) {
-		hlist_del_init_rcu(&p->mnt_hash);
 		list_del_init(&p->mnt_child);
 	}
 
@@ -1367,6 +1369,7 @@ static void umount_tree(struct mount *mn
 			p->mnt_mountpoint = p->mnt.mnt_root;
 			p->mnt_parent = p;
 			p->mnt_mp = NULL;
+			hlist_del_init_rcu(&p->mnt_hash);
 		}
 		change_mnt_propagation(p, MS_PRIVATE);
 	}
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -383,7 +383,6 @@ static void __propagate_umount(struct mo
 		 */
 		if (child && list_empty(&child->mnt_mounts)) {
 			list_del_init(&child->mnt_child);
-			hlist_del_init_rcu(&child->mnt_hash);
 			child->mnt.mnt_flags |= MNT_UMOUNT;
 			list_move_tail(&child->mnt_list, &mnt->mnt_list);
 		}


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