Patch "mnt: Don't propagate unmounts to locked mounts" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

mnt: Don't propagate unmounts to locked mounts

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mnt-don-t-propagate-unmounts-to-locked-mounts.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Eric W. Biederman" <[email protected]>
Date: Mon, 5 Jan 2015 13:38:04 -0600
Subject: mnt: Don't propagate unmounts to locked mounts

From: "Eric W. Biederman" <[email protected]>

commit 0c56fe31420ca599c90240315f7959bf1b4eb6ce upstream.

If the first mount in shared subtree is locked don't unmount the shared subtree.

This is ensured by walking through the mounts parents before children and marking a mount as unmountable if it is not locked or it is locked but it's parent is marked.

This allows recursive mount detach to propagate through a set of mounts when unmounting them would not reveal what is under any locked mount.

---
 fs/pnode.c |   32 +++++++++++++++++++++++++++++---
 fs/pnode.h |    1 +
 2 files changed, 30 insertions(+), 3 deletions(-)

@@ -382,6 +382,26 @@ void propagate_mount_unlock(struct mount
 }
 
 /*
+ * Mark all mounts that the MNT_LOCKED logic will allow to be unmounted.
+ */
+static void mark_umount_candidates(struct mount *mnt)
+{
+	struct mount *parent = mnt->mnt_parent;
+	struct mount *m;
+
+	BUG_ON(parent == mnt);
+
+	for (m = propagation_next(parent, parent); m;
+			m = propagation_next(m, parent)) {
+		struct mount *child = __lookup_mnt_last(&m->mnt,
+						mnt->mnt_mountpoint);
+		if (child && (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m))) {
+			SET_MNT_MARK(child);
+		}
+	}
+}
+
+/*
  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
  * parent propagates to.
  */

@@ -398,10 +418,13 @@ static void __propagate_umount(struct mo
 		struct mount *child = __lookup_mnt_last(&m->mnt,
 						mnt->mnt_mountpoint);
 		/*
-		 * umount the child only if the child has no
-		 * other children
+		 * umount the child only if the child has no children
+		 * and the child is marked safe to unmount.
 		 */
-		if (child && list_empty(&child->mnt_mounts)) {
+		if (!child || !IS_MNT_MARKED(child))
+			continue;
+		CLEAR_MNT_MARK(child);
+		if (list_empty(&child->mnt_mounts)) {
 			list_del_init(&child->mnt_child);
 			child->mnt.mnt_flags |= MNT_UMOUNT;
 			list_move_tail(&child->mnt_list, &mnt->mnt_list);

@@ -420,6 +443,9 @@ int propagate_umount(struct list_head *l
 {
 	struct mount *mnt;
 
+	list_for_each_entry_reverse(mnt, list, mnt_list)
+		mark_umount_candidates(mnt);
+
 	list_for_each_entry(mnt, list, mnt_list)
 		__propagate_umount(mnt);
 	return 0;

@@ -19,6 +19,7 @@
 #define IS_MNT_MARKED(m) ((m)->mnt.mnt_flags & MNT_MARKED)
 #define SET_MNT_MARK(m) ((m)->mnt.mnt_flags |= MNT_MARKED)
 #define CLEAR_MNT_MARK(m) ((m)->mnt.mnt_flags &= ~MNT_MARKED)
+#define IS_MNT_LOCKED(m) ((m)->mnt.mnt_flags & MNT_LOCKED)
 
 #define CL_EXPIRE    		0x01
 #define CL_SLAVE     		0x02

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/mnt-don-t-propagate-umounts-in-__detach_mounts.patch queue-4.0/mnt-add-mnt_umount-flag.patch queue-4.0/mnt-honor-mnt_locked-when-detaching-mounts.patch queue-4.0/mnt-delay-removal-from-the-mount-hash.patch queue-4.0/mnt-on-an-unmount-propagate-clearing-of-mnt_locked.patch queue-4.0/mnt-don-t-propagate-unmounts-to-locked-mounts.patch queue-4.0/mnt-factor-out-unhash_mnt-from-detach_mnt-and-umount_tree.patch queue-4.0/mnt-factor-umount_mnt-from-umount_tree.patch queue-4.0/mnt-fix-the-error-check-in-__detach_mounts.patch queue-4.0/mnt-update-detach_mounts-to-leave-mounts-connected.patch queue-4.0/mnt-improve-the-umount_tree-flags.patch queue-4.0/mnt-in-umount_tree-reuse-mnt_list-instead-of-mnt_hash.patch