Commit d579b04a authored by Yu-Ting Tseng's avatar Yu-Ting Tseng Committed by Greg Kroah-Hartman
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binder: frozen notification 

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: default avatarYu-Ting Tseng <yutingtseng@google.com>
Acked-by: default avatarCarlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20240709070047.4055369-4-yutingtseng@google.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 104831a1
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