Re: [PATCH V3] binder: ipc namespace support for android binder

[Todd Kjos]

On Fri, Nov 9, 2018 at 10:27 AM Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote:
>
> On Thu, 08 Nov 2018, chouryzhou(??????) wrote:
>
> >+#ifdef CONFIG_ANDROID_BINDER_IPC
> >+       /* next fields are for binder */
> >+       struct mutex      binder_procs_lock;
> >+       struct hlist_head binder_procs;
> >+       struct hlist_head binder_contexts;
> >+#endif
>
> Now, I took a look at how the binder_procs list is used; and no, what
> follows isn't really related to this patch, but a general observation.
>
> I think that a mutex is also an overkill and you might wanna replace it
> with a spinlock/rwlock. Can anything block while holding the binder_procs_lock?
> I don't see anything... you mainly need it for consulting the hlist calling
> print_binder_proc[_stat]() - which will take the proc->inner_lock anyway, so
> no blocking there.

print_binder_proc() drops proc->inner_lock and calls
binder_alloc_print_allocated() which acquires proc->alloc->mutex.
Likewise, print_binder_stats() calls print_binder_proc_stats() which
drops its locks to call binder_alloc_print_pages() which also acquires
proc->alloc->mutex. So binder_procs_lock needs to be a mutex since it
can block on proc->alloc->mutex.

> Also, if this is perhaps because of long hold times, dunno,
> the rb_first_cached primitive might reduce some of it, although I don't know
> how big the rbtrees in binder can get and if it matters at all.
>
> Anyway, that said and along with addressing Todd's comments, the ipc/ bits look
> good. Feel free to add my:
>
> Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
>
> Thanks,
> Davidlohr