In (e)poll mode, threads often depend on I/O events to determine when data is ready for consumption. Within binder, a thread may initiate a command via BINDER_WRITE_READ without a read buffer and then make use of epoll_wait() or similar to consume any responses afterwards.
It is then crucial that epoll threads are signaled via wakeup when they queue their own work. Otherwise, they risk waiting indefinitely for an event leaving their work unhandled. What is worse, subsequent commands won't trigger a wakeup either as the thread has pending work.
Fixes: 457b9a6f09f0 ("Staging: android: add binder driver") Cc: Arve Hjønnevåg arve@android.com Cc: Martijn Coenen maco@android.com Cc: Alice Ryhl aliceryhl@google.com Cc: Steven Moreland smoreland@google.com Cc: stable@vger.kernel.org # v4.19+ Signed-off-by: Carlos Llamas cmllamas@google.com --- drivers/android/binder.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 8dd23b19e997..eca24f41556d 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -478,6 +478,16 @@ binder_enqueue_thread_work_ilocked(struct binder_thread *thread, { WARN_ON(!list_empty(&thread->waiting_thread_node)); binder_enqueue_work_ilocked(work, &thread->todo); + + /* (e)poll-based threads require an explicit wakeup signal when + * queuing their own work; they rely on these events to consume + * messages without I/O block. Without it, threads risk waiting + * indefinitely without handling the work. + */ + if (thread->looper & BINDER_LOOPER_STATE_POLL && + thread->pid == current->pid && !thread->process_todo) + wake_up_interruptible_sync(&thread->wait); + thread->process_todo = true; }