From: Eric Biggers ebiggers@google.com
commit a880b28a71e39013e357fd3adccd1d8a31bc69a8 upstream.
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 --- drivers/android/binder.c | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 9229c5c9ad473..35c13be4adc60 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -4416,23 +4416,20 @@ static int binder_thread_release(struct binder_proc *proc, }
/* - * 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();