linux-kernel - Re: [PATCH] random: Don't freeze in add_hwgenerator

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Message-ID: <2f581f84-378f-05cf-1902-f0494aafe706@nxp.com>
Date:   Wed, 2 Dec 2020 16:28:07 +0200
From:   Horia Geantă <horia.geanta@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc:     Stephen Boyd <swboyd@...omium.org>, Theodore Ts'o <tytso@....edu>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Keerthy <j-keerthy@...com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] random: Don't freeze in add_hwgenerator_randomness() if
 stopping kthread

On 11/17/2019 2:57 AM, Herbert Xu wrote:
> On Sun, Nov 17, 2019 at 12:01:20AM +0100, Maciej S. Szmigiero wrote:
>>
>> If a reader (user space) task is frozen then it is no longer waiting
>> on this waitqueue - at least if I understand correctly how the freezer
>> works for user space tasks, that is by interrupting waits via a fake
>> signal.
> 
> At this point I'm just going to revert the whole thing and we can
> sort it out in the next development cycle.
> 
Working at adding power management support for caam crypto driver,
I've stumbled upon the issue of caam rng suspending while hwrng kthread
is still active.

For now I've fixed the issue by unregistering / re-registering caam rng
from hwrng at device suspend / resume time.

OTOH I see a few commits:
03a3bb7ae631 ("hwrng: core - Freeze khwrng thread during suspend")
ff296293b353 ("random: Support freezable kthreads in add_hwgenerator_randomness()")
59b569480dc8 ("random: Use wait_event_freezable() in add_hwgenerator_randomness()")

however they were reverted a bit later in commit
08e97aec700a ("Revert "hwrng: core - Freeze khwrng thread during suspend"")

I wasn't able to find a follow-up on this topic.
Could you advise on what's the proper thing to do going forward?

Thanks,
Horia