linux-kernel - Re: [PATCH RESEND] lib/test_printf.c: call wait_for_random

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Date:   Fri, 22 Jun 2018 23:50:20 +0200
From:   Thierry Escande <thierry.escande@...aro.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Miller <davem@...emloft.net>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH RESEND] lib/test_printf.c: call wait_for_random_bytes()
 before plain %p tests

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This patch has been superseded with a v2 and a v3 pushed into Petr 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@...aro.org>
>>> Acked-by: Tobin C. Harding <me@...in.cc>
>>> ---
>>>   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
>>>