5.4-stable review patch. If anyone has any objections, please let me know.
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From: Carlos Llamas cmllamas@google.com
commit 97830f3c3088638ff90b20dfba2eb4d487bf14d7 upstream.
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 Link: https://lore.kernel.org/r/20240131215347.1808751-1-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/android/binder.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -840,6 +840,16 @@ binder_enqueue_thread_work_ilocked(struc { 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; }