In case when we mounting something on top of a large stack of overmounts,
all of them being peers of each other, we get quadratic time by the
depth of overmount stack. Easily fixed by doing commit_tree() before
reparenting the overmount; simplifies commit_tree() as well - it doesn't
need to skip the already mounted stuff that had been reparented on top
of the new mounts.
Since we are holding mount_lock through both reparenting and call of
commit_tree(), the order does not matter from the mount hash point
of view.
Reported-by: "Lai, Yi" <yi1.lai@xxxxxxxxxxxxxxx>
Tested-by: "Lai, Yi" <yi1.lai@xxxxxxxxxxxxxxx>
Fixes: 663206854f02 "copy_tree(): don't link the mounts via mnt_list"
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
fs/namespace.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index ddfd4457d338..1c97f93d1865 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1197,10 +1197,7 @@ static void commit_tree(struct mount *mnt)
if (!mnt_ns_attached(mnt)) {
for (struct mount *m = mnt; m; m = next_mnt(m, mnt))
- if (unlikely(mnt_ns_attached(m)))
- m = skip_mnt_tree(m);
- else
- mnt_add_to_ns(n, m);
+ mnt_add_to_ns(n, m);
n->nr_mounts += n->pending_mounts;
n->pending_mounts = 0;
}
@@ -2704,6 +2701,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
lock_mnt_tree(child);
q = __lookup_mnt(&child->mnt_parent->mnt,
child->mnt_mountpoint);
+ commit_tree(child);
if (q) {
struct mountpoint *mp = root.mp;
struct mount *r = child;
@@ -2713,7 +2711,6 @@ static int attach_recursive_mnt(struct mount *source_mnt,
mp = shorter;
mnt_change_mountpoint(r, mp, q);
}
- commit_tree(child);
}
unpin_mountpoint(&root);
unlock_mount_hash();
--
2.47.2
