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Frozen processes present a significant challenge in binder transactions. When a process is frozen, it cannot, by design, accept and/or respond to binder transactions. As a result, the sender needs to adjust its behavior, such as postponing transactions until the peer process unfreezes. However, there is currently no way to subscribe to these state change events, making it impossible to implement frozen-aware behaviors efficiently. Introduce a binder API for subscribing to frozen state change events. This allows programs to react to changes in peer process state, mitigating issues related to binder transactions sent to frozen processes. Implementation details: For a given binder_ref, the state of frozen notification can be one of the followings: 1. Userspace doesn't want a notification. binder_ref->freeze is null. 2. Userspace wants a notification but none is in flight. list_empty(&binder_ref->freeze->work.entry) = true 3. A notification is in flight and waiting to be read by userspace. binder_ref_freeze.sent is false. 4. A notification was read by userspace and kernel is waiting for an ack. binder_ref_freeze.sent is true. When a notification is in flight, new state change events are coalesced into the existing binder_ref_freeze struct. If userspace hasn't picked up the notification yet, the driver simply rewrites the state. Otherwise, the notification is flagged as requiring a resend, which will be performed once userspace acks the original notification that's inflight. See https://r.android.com/3070045 for how userspace is going to use this feature. Signed-off-by: Yu-Ting Tseng <yutingtseng@google.com> Acked-by: Carlos Llamas <cmllamas@google.com> Link: https://lore.kernel.org/r/20240709070047.4055369-4-yutingtseng@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.