diff mbox

[3.13.y.z,extended,stable] Patch "fix EBUSY on umount() from MNT_SHRINKABLE" has been added to staging queue

Message ID 1412112585-26363-1-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa Sept. 30, 2014, 9:29 p.m. UTC 
This is a note to let you know that I have just added a patch titled

    fix EBUSY on umount() from MNT_SHRINKABLE

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.8.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

From 9015517daebabd2c29b50242fdae7de8b8e41331 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sat, 30 Aug 2014 18:32:05 -0400
Subject: fix EBUSY on umount() from MNT_SHRINKABLE

commit 81b6b06197606b4bef4e427a197aeb808e8d89e1 upstream.

We need the parents of victims alive until namespace_unlock() gets to
dput() of the (ex-)mountpoints.  However, that screws up the "is it
busy" checks in case when we have shrinkable mounts that need to be
killed.  Solution: go ahead and decrement refcounts of parents right
in umount_tree(), increment them again just before dropping rwsem in
namespace_unlock() (and let the loop in the end of namespace_unlock()
finally drop those references for good, as we do now).  Parents can't
get freed until we drop rwsem - at least one reference is kept until
then, both in case when parent is among the victims and when it is
not.  So they'll still be around when we get to namespace_unlock().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 fs/namespace.c | 6 ++++++
 1 file changed, 6 insertions(+)

--
1.9.1
diff mbox

Patch

diff --git a/fs/namespace.c b/fs/namespace.c
index a93e25a..b1af425 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1217,6 +1217,11 @@  static void namespace_unlock(void)
 	head.first->pprev = &head.first;
 	INIT_HLIST_HEAD(&unmounted);

+	/* undo decrements we'd done in umount_tree() */
+	hlist_for_each_entry(mnt, &head, mnt_hash)
+		if (mnt->mnt_ex_mountpoint.mnt)
+			mntget(mnt->mnt_ex_mountpoint.mnt);
+
 	up_write(&namespace_sem);

 	synchronize_rcu();
@@ -1268,6 +1273,7 @@  void umount_tree(struct mount *mnt, int how)
 			p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
 		if (mnt_has_parent(p)) {
 			put_mountpoint(p->mnt_mp);
+			mnt_add_count(p->mnt_parent, -1);
 			/* move the reference to mountpoint into ->mnt_ex_mountpoint */
 			p->mnt_ex_mountpoint.dentry = p->mnt_mountpoint;
 			p->mnt_ex_mountpoint.mnt = &p->mnt_parent->mnt;