diff mbox series

binder: signal epoll threads of self-work

Message ID 20240131215347.1808751-1-cmllamas@google.com
State New
Headers
Series binder: signal epoll threads of self-work |

Commit Message

Carlos Llamas Jan. 31, 2024, 9:53 p.m. UTC 
  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 mbox series

Patch

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;
 }