binder: use wake_up_pollfree()

wake_up_poll() uses nr_exclusive=1, so it's not guaranteed to wake up
all exclusive waiters.  Yet, POLLFREE *must* wake up all waiters.  epoll
and aio poll are fortunately not affected by this, but it's very
fragile.  Thus, the new function wake_up_pollfree() has been introduced.

Convert binder to use wake_up_pollfree().

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Fixes: f5cb779ba163 ("ANDROID: binder: remove waitqueue when thread exits.")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211209010455.42744-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index cffbe57a8e08637c32db0f8dede33a26c9b88277..c75fb600740cc1ee5c97598c090f658324d3e722 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4422,23 +4422,20 @@ static int binder_thread_release(struct binder_proc *proc,
        __release(&t->lock);
 
        /*
-        * If this thread used poll, make sure we remove the waitqueue
-        * from any epoll data structures holding it with POLLFREE.
-        * waitqueue_active() is safe to use here because we're holding
-        * the inner lock.
+        * If this thread used poll, make sure we remove the waitqueue from any
+        * poll data structures holding it.
         */
-       if ((thread->looper & BINDER_LOOPER_STATE_POLL) &&
-           waitqueue_active(&thread->wait)) {
-               wake_up_poll(&thread->wait, EPOLLHUP | POLLFREE);
-       }
+       if (thread->looper & BINDER_LOOPER_STATE_POLL)
+               wake_up_pollfree(&thread->wait);
 
        binder_inner_proc_unlock(thread->proc);
 
        /*
-        * This is needed to avoid races between wake_up_poll() above and
-        * and ep_remove_waitqueue() called for other reasons (eg the epoll file
-        * descriptor being closed); ep_remove_waitqueue() holds an RCU read
-        * lock, so we can be sure it's done after calling synchronize_rcu().
+        * This is needed to avoid races between wake_up_pollfree() above and
+        * someone else removing the last entry from the queue for other reasons
+        * (e.g. ep_remove_wait_queue() being called due to an epoll file
+        * descriptor being closed).  Such other users hold an RCU read lock, so
+        * we can be sure they're done after we call synchronize_rcu().
         */
        if (thread->looper & BINDER_LOOPER_STATE_POLL)
                synchronize_rcu();