binder: signal epoll threads of self-work
Subsystems (2)
Carlos Llamas
maintainerPATCH 1/1 binder: signal epoll threads of self-work
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 <[email protected]>
Cc Martijn Coenen <[email protected]>
Cc Alice Ryhl <[email protected]>
Cc Steven Moreland <[email protected]>
Cc <[email protected]> # v4.19+
Signed-off-by Carlos Llamas <[email protected]>
--- drivers/android/binder.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
drivers/android/binder.c +10 -0
@@ -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; }
Signature · 1 line
2.43.0.594.gd9cf4e227d-goog