Re: [PATCH v3 2/2] rust_binder: account for deferred work size in Thread::read()

[Carlos Llamas <cmllamas@google.com>]

On Wed, Nov 11, 2026 at 05:23:24PM +0000, Chris Wiseman wrote:
> When a looper thread replies with TF_DEFER_COMPLETE, its 4-byte
> BR_TRANSACTION_COMPLETE work item is queued via push_work_deferred() in
> inner.work_list without setting inner.process_work_list. On the next
> blocking BINDER_WRITE_READ ioctl, inner.should_use_process_work_queue()
> returns true and Thread::read() checks only whether the remaining output
> buffer can fit a single transaction (4-byte command code plus
> size_of::<uapi::binder_transaction_data_secctx>()).
> 
> If userspace provides a read buffer with 76 bytes remaining after the
> initial 4-byte BR_NOOP placeholder (read_size = 80), Thread::read()
> calls Self::get_work(), sleeps in Process.ready_threads, and receives an
> incoming synchronous transaction queued behind the deferred
> BR_TRANSACTION_COMPLETE in inner.work_list. Iteration 1 of the loop
> writes the 4-byte BR_TRANSACTION_COMPLETE, reducing writer.len() to 72
> bytes, and iteration 2 exits the loop without delivering the incoming
> transaction, leaving it stranded in the thread-local work_list.
> 
> Add a size(&self) -> usize method to DeliverToRead returning the maximum
> number of bytes that do_work() may write to the user read buffer, and
> add InnerThread::pop_deferred_work() and Thread::pop_deferred_work() to
> drain deferred items from inner.work_list before entering the main work
> loop in Thread::read() when the remaining buffer is at least 76 bytes
> but cannot fit both the queued deferred items and an incoming
> transaction. If any deferred item writes bytes to the buffer, skip the
> main work loop and return the drained deferred items immediately without
> mutating inner.process_work_list or waiting for new work.
> 
> Suggested-by: Alice Ryhl <aliceryhl@google.com>
> Fixes: 8eb05e8e47f1 ("rust_binder: add TF_DEFER_COMPLETE flag for avoiding userspace roundtrip")
> Cc: stable@vger.kernel.org
> Signed-off-by: Chris Wiseman <chriswiseman@google.com>
> ---

Aside from the "patch threading" issue, this LGTM. Thanks!

Acked-by: Carlos Llamas <cmllamas@google.com>