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From:   Li Li <dualli@chromium.org>
Date:   Thu, 11 Mar 2021 01:36:26 -0800
Message-ID: <CA+xfxX4tD30BJLgwLAoiMzF7xTC-4q1i0A5Znp3tJzyi3ATLzQ@mail.gmail.com>
Subject: Re: [PATCH v1 1/3] binder: BINDER_FREEZE ioctl
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Todd Kjos <tkjos@google.com>, christian@brauner.io,
        arve@android.com, devel@driverdev.osuosl.org,
        linux-kernel@vger.kernel.org, Martijn Coenen <maco@google.com>,
        hridya@google.com, surenb@google.com, joel@joelfernandes.org,
        kernel-team@android.com
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On Wed, Mar 10, 2021 at 11:33 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Wed, Mar 10, 2021 at 02:52:49PM -0800, Li Li wrote:
> >       if (target_proc) {
> >               binder_inner_proc_lock(target_proc);
> > +             target_proc->outstanding_txns--;
> > +             WARN_ON(target_proc->outstanding_txns < 0);
>
> WARN_* is a huge crutch, please just handle stuff like this properly and
> if you really need to, warn userspace (but what can they do about it?)
>
> You also just rebooted all systems that have panic-on-warn set, so if
> this can be triggered by userspace, you caused a DoS of things :(
>
> So please remove all of the WARN_ON() you add in this patch series to
> properly handle the error conditions and deal with them correctly.
>
> And if these were here just for debugging, hopefully the code works
> properly now and you do not need debugging anymore so they can all just
> be dropped.

When the target_proc is freed, there's no outstanding transactions already.
The FREEZE ioctl from userspace won't trigger this. It's for debugging.
And I'll remove it in v2. Thanks for the suggestion!