This is a note to let you know that I've just added the patch titled
fix EBUSY on umount() from MNT_SHRINKABLE
to the 3.16-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:
fix-ebusy-on-umount-from-mnt_shrinkable.patch
and it can be found in the queue-3.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 81b6b06197606b4bef4e427a197aeb808e8d89e1 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Sat, 30 Aug 2014 18:32:05 -0400
Subject: fix EBUSY on umount() from MNT_SHRINKABLE
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/namespace.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1226,6 +1226,11 @@ 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();
@@ -1277,6 +1282,7 @@ void umount_tree(struct mount *mnt, int
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;
Patches currently in stable-queue which might be from viro@xxxxxxxxxxxxxxxxxx are
queue-3.16/fix-ebusy-on-umount-from-mnt_shrinkable.patch
queue-3.16/get-rid-of-propagate_umount-mistakenly-treating-slaves-as-busy.patch
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