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

[Thierry Escande]

On 22/06/2018 22:53, Steven Rostedt wrote:
> On Thu, Jun 07, 2018 at 02:24:34PM +0200, 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
>
> And neither does my test box. It killed my tests I was running, as one of the
> configs I test has this set.
>
> It appears that Andrew pulled it in and sent it to Linus, as it is in
> 4.18-rc1, and I need to now revert this patch to make my tests work.

This patch has been superseded with a v2 and a v3 pushed into Petr 
printk.git tree 
(https://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk.git/commit/?h=for-4.19&id=ce041c43f22298485122bab15c14d062383fbc67). 
Sorry for the mess...

Regards,
Thierry

> -- Steve
>
>
> > 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.
> >
> > 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