percpu_ref_init(): clean ->percpu_count_ref on failure

That way percpu_ref_exit() is safe after failing percpu_ref_init().
At least one user (cgroup_create()) had a double-free that way;
there might be other similar bugs.  Easier to fix in percpu_ref_init(),
rather than playing whack-a-mole in sloppy users...

Usual symptoms look like a messed refcounting in one of subsystems
that use percpu allocations (might be percpu-refcount, might be
something else).  Having refcounts for two different objects share
memory is Not Nice(tm)...

Reported-by: syzbot+5b1e53987f858500ec00@syzkaller.appspotmail.com
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index af9302141bcf63983b8bac15468174f63ed0edc7..e5c5315da274194e5f8f35b5e9735551c030e5a8 100644 (file)
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -76,6 +76,7 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
        data = kzalloc(sizeof(*ref->data), gfp);
        if (!data) {
                free_percpu((void __percpu *)ref->percpu_count_ptr);
+               ref->percpu_count_ptr = 0;
                return -ENOMEM;
        }