linux-kernel - Re: [PATCH v2 6/8] binder: allow freeze notification for dead nodes

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Message-ID: <ZwV1-svdRZCF2x2H@google.com>
Date: Tue, 8 Oct 2024 18:12:10 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Yu-Ting Tseng <yutingtseng@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Christian Brauner <brauner@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	stable@...r.kernel.org
Subject: Re: [PATCH v2 6/8] binder: allow freeze notification for dead nodes

On Mon, Sep 30, 2024 at 03:30:01PM +0200, Alice Ryhl wrote:
> On Fri, Sep 27, 2024 at 6:32 PM Carlos Llamas <cmllamas@...gle.com> wrote:
> >
> > There are different ways to proceed with this dead node scenario:
> >
> > 1. return ESRCH
> > 2. silently fail and don't allocate a ref->freeze
> > 3. allocate a ref->freeze but don't notify the current state
> > 4. allocate and send a "fake" state notification.
> >
> > I like 1 just because it is technically the correct thing to do from the
> > driver's perspective. However, it does complicate things in userspace as
> > we've discussed. Option 2, could work but it would also fail with EINVAL
> > if a "clear notification" is sent later anyway. Option 3 changes the
> > behavior of guaranteeing a notification upon success. Option 4 can cause
> > trouble on how a "not-frozen" notification is handled in userspace e.g
> > start sending transactions.
> >
> > As you can see there is no clear winner here, we have to compromise
> > something and option #3 is the best we can do IMO.
> 
> I am happy with both #3 and #4. I think #1 and #2 are problematic
> because they will lead to userspace getting errors on correct use of
> Binder.

After talking with userspace folks it seems that #3 would be their
preferred approach. So this v2 patch it the way to go then!

Thanks,
Carlos Llamas