linux-kernel - Re: [PATCH v2 1/3] rust_binder: freeze_notif

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Message-ID: <aOaTgDMY-VvM_r6m@google.com>
Date: Wed, 8 Oct 2025 16:38:24 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Christian Brauner <brauner@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 1/3] rust_binder: freeze_notif_done should resend if
 wrong state

On Wed, Oct 08, 2025 at 06:34:54PM +0200, Alice Ryhl wrote:
> On Wed, Oct 8, 2025 at 6:32 PM Carlos Llamas <cmllamas@...gle.com> wrote:
> >
> > On Tue, Oct 07, 2025 at 09:39:51AM +0000, Alice Ryhl wrote:
> > > Consider the following scenario:
> > > 1. A freeze notification is delivered to thread 1.
> > > 2. The process becomes frozen or unfrozen.
> > > 3. The message for step 2 is delivered to thread 2 and ignored because
> > >    there is already a pending notification from step 1.
> > > 4. Thread 1 acknowledges the notification from step 1.
> > > In this case, step 4 should ensure that the message ignored in step 3 is
> > > resent as it can now be delivered.
> >
> > hmmm, I wonder what happens with 3 threads involved where the state goes
> > back to the (unconsumed) initial freeze notification. Userspace will
> > probably see two separate notifications of the same state?
> 
> The way I implemented it, the work items report the current state when
> the work item is *executed*, and they do nothing if there's no change
> since last notification.

Oh I see, then that means the 2nd and 3rd notifications would do nothing
as the state went back to the last notification, correct?