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

From: Thierry Escande
Date: Thu Jun 07 2018 - 14:47:33 EST

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

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?


Best Regards,

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");