On Thu, Sep 9, 2021 at 10:38 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, Sep 09, 2021 at 08:53:16PM -0700, Li Li wrote:
> > struct binder_frozen_status_info {
> > __u32 pid;
> > +
> > + /* process received sync transactions since last frozen
> > + * bit 0: received sync transaction after being frozen
> > + * bit 1: new pending sync transaction during freezing
> > + */
> > __u32 sync_recv;
>
> You just changed a user/kernel api here, did you just break existing
> userspace applications? If not, how did that not happen?
>
That's a good question. This design does keep backward compatibility.
The existing userspace applications call ioctl(BINDER_GET_FROZEN_INFO)
to check if there's sync or async binder transactions sent to a frozen
process.
If the existing userspace app runs on a new kernel, a sync binder call
still sets bit 1 of sync_recv (as it's a bool variable) so the ioctl
will return the expected value (TRUE). The app just doesn't check bit
1 intentionally so it doesn't have the ability to tell if there's a
race - this behavior is aligned with what happens on an old kernel as
the old kernel doesn't have bit 1 set at all.
The bit 1 of sync_recv enables new userspace app the ability to tell
1) there's a sync binder transaction happened when being frozen - same
as before; and 2) if that sync binder transaction happens exactly when
there's a race - a new information for rollback decision.
> thanks,
>
> greg k-h
Thanks,
Li
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