Re: [PATCH RESEND] lib/test_printf.c: call wait_for_random_bytes() before plain %p tests

[Thierry Escande]

Hi Petr,

On 07/06/2018 14:24, Petr Mladek wrote:
> On Mon 2018-06-04 13:37:08, Thierry Escande wrote:
> > If the test_printf module is loaded before the crng is initialized, the
> > plain 'p' tests will fail because the printed address will not be hashed
> > and the buffer will contain '(ptrval)' instead.
> > This patch adds a call to wait_for_random_bytes() before plain 'p' tests
> > to make sure the crng is initialized.
>
> Hmm, my system did not boot with this patch and
> CONFIG_TEST_PRINTF=y
>
> I guess that there was not enough entropy. It is basically a deadlock.
> The build-in module init calls are called when SMP is enabled but
> there is no real activity and the init calls are called sequentially.
> Therefore there is nothing that could produce some entropy, ...
>
> I suggest to skip the test when crng is not ready.

Thanks for pointing this out.

The issue is that the crng_ready() is not available outside of random.c. 
I'll leave the call to wait_for_random_bytes() if test_printf is 
compiled as a module and use add_random_ready_callback() to check if 
crng is initialized otherwise. Does that sound ok to you?

Regards,
Thierry

> Best Regards,
> Petr
>
> > Signed-off-by: Thierry Escande <thierry.escande@xxxxxxxxxx>
> > Acked-by: Tobin C. Harding <me@xxxxxxxx>
> > ---
> >   lib/test_printf.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/lib/test_printf.c b/lib/test_printf.c
> > index 71ebfa43ad05..839be9385a8a 100644
> > --- a/lib/test_printf.c
> > +++ b/lib/test_printf.c
> > @@ -260,6 +260,13 @@ plain(void)
> >   {
> >   	int err;
> >   
> > +	/*
> > +	 * Make sure crng is ready. Otherwise we get "(ptrval)" instead
> > +	 * of a hashed address when printing '%p' in plain_hash() and
> > +	 * plain_format().
> > +	 */
> > +	wait_for_random_bytes();
> > +
> >   	err = plain_hash();
> >   	if (err) {
> >   		pr_warn("plain 'p' does not appear to be hashed\n");
> > --
> > 2.14.1