From 97830f3c3088638ff90b20dfba2eb4d487bf14d7 Mon Sep 17 00:00:00 2001 From: Carlos Llamas Date: Wed, 31 Jan 2024 21:53:46 +0000 Subject: [PATCH] binder: signal epoll threads of self-work MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Cc: Martijn Coenen Cc: Alice Ryhl Cc: Steven Moreland Cc: stable@vger.kernel.org # v4.19+ Signed-off-by: Carlos Llamas Link: https://lore.kernel.org/r/20240131215347.1808751-1-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman --- 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; }