[Devel] [PATCH RHEL7 COMMIT] Revert "revert rh mnt: Honor MNT_LOCKED when detaching mounts"

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.1.1.vz7.37.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.1.1.vz7.37.5
------>
commit 15b70fe6002927ab5929740a277b5b4280515669
Author: Konstantin Khorenko <khorenko at virtuozzo.com>
Date:   Mon Sep 18 12:12:11 2017 +0300

    Revert "revert rh mnt: Honor MNT_LOCKED when detaching mounts"
    
    This reverts commit 0573dc863a9ef9a7c5cba27c8a35c415c7174ae1.
    
    This was a temporary fix for
    https://jira.sw.ru/browse/PSBM-71414
    
    The issue will be fixed by next patch.
    
    Signed-off-by:	Vasily Averin <vvs at virtuozzo.com>
---
 fs/namespace.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 52 insertions(+), 3 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 6dbf827..2c98249 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1125,6 +1125,13 @@ static void mntput_no_expire(struct mount *mnt)
 	rcu_read_unlock();
 
 	list_del(&mnt->mnt_instance);
+
+	if (unlikely(!list_empty(&mnt->mnt_mounts))) {
+		struct mount *p, *tmp;
+		list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
+			umount_mnt(p);
+		}
+	}
 	unlock_mount_hash();
 
 	if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
@@ -1399,6 +1406,35 @@ enum umount_tree_flags {
 	UMOUNT_CONNECTED = 4,
 };
 
+static bool disconnect_mount(struct mount *mnt, enum umount_tree_flags how)
+{
+	/* Leaving mounts connected is only valid for lazy umounts */
+	if (how & UMOUNT_SYNC)
+		return true;
+
+	/* A mount without a parent has nothing to be connected to */
+	if (!mnt_has_parent(mnt))
+		return true;
+
+	/* Because the reference counting rules change when mounts are
+	 * unmounted and connected, umounted mounts may not be
+	 * connected to mounted mounts.
+	 */
+	if (!(mnt->mnt_parent->mnt.mnt_flags & MNT_UMOUNT))
+		return true;
+
+	/* Has it been requested that the mount remain connected? */
+	if (how & UMOUNT_CONNECTED)
+		return false;
+
+	/* Is the mount locked such that it needs to remain connected? */
+	if (IS_MNT_LOCKED(mnt))
+		return false;
+
+	/* By default disconnect the mount */
+	return true;
+}
+
 /*
  * mount_lock must be held
  * namespace_sem must be held for write
@@ -1427,6 +1463,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 		propagate_umount(&tmp_list);
 
 	while (!list_empty(&tmp_list)) {
+		bool disconnect;
 		p = list_first_entry(&tmp_list, struct mount, mnt_list);
 		list_del_init(&p->mnt_expire);
 		list_del_init(&p->mnt_list);
@@ -1435,10 +1472,18 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 		if (how & UMOUNT_SYNC)
 			p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
 
-		pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt, &unmounted);
+		disconnect = disconnect_mount(p, how);
+
+		pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
+				 disconnect ? &unmounted : NULL);
 		if (mnt_has_parent(p)) {
 			mnt_add_count(p->mnt_parent, -1);
-			umount_mnt(p);
+			if (!disconnect) {
+				/* Don't forget about p */
+				list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
+			} else {
+				umount_mnt(p);
+			}
 		}
 		change_mnt_propagation(p, MS_PRIVATE);
 	}
@@ -1566,7 +1611,11 @@ void __detach_mounts(struct dentry *dentry)
 	event++;
 	while (!hlist_empty(&mp->m_list)) {
 		mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
-		umount_tree(mnt, UMOUNT_CONNECTED);
+		if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
+			hlist_add_head(&mnt->mnt_umount.s_list, &unmounted);
+			umount_mnt(mnt);
+		}
+		else umount_tree(mnt, UMOUNT_CONNECTED);
 	}
 	put_mountpoint(mp);
 out_unlock: