linux-kernel - Re: [PATCH 0/3] staging: vchiq: use interruptible waits

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Message-ID: <762bb0f7-b9d1-3182-524b-6cdec87a08f8@i2se.com>
Date:   Fri, 5 Apr 2019 14:40:27 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     devel@...verdev.osuosl.org, phil@...pberrypi.org,
        linux-kernel@...r.kernel.org, eric@...olt.net,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/3] staging: vchiq: use interruptible waits

Hi Nicolas,

Am 05.04.19 um 13:34 schrieb Nicolas Saenz Julienne:
> Hi,
> this series tries to address an issue that came up in Raspbian's kernel
> tree [1]. After pulling from upstream some changes that moved wait calls
> from a custom implementation to the more standard killable family some
> users complained that all the VCHIQ threads showed up in D state (which
> is the expected behaviour).

this issue has already been noticed in mainline distributions [1],[2].

> The custom implementation we deleted tried to mimic the killable family
> of functions, yet accepted more signals than the later.  SIGKILL |
> SIGINT | SIGQUIT | SIGTRAP | SIGSTOP | SIGCONT for the custom
> implementation as opposed to plain old SIGKILL.
>
> Raspbian maintainers decided roll back some of those changes and leave
> the wait functions as interruptible. Hence creating some divergence
> between both trees.
>
> One could argue that not liking having the threads stuck in D state is
> not really a software issue. It's more a cosmetic thing that can scare
> people when they look at "uptime". On the other hand, if we are ever to
> unstage this driver, we'd really need a proper justification for using
> the killable family of functions. Which I think it's not really clear at
> the moment.

I like to see this decision as a short comment in the code to prevent
other for doing this mistake again.

Thanks

Stefan

>
> As Raspbian's kernel has been working for a while with interruptible
> waits I propose we follow through. If needed we can always go back to
> killable. But at least we'll have a proper understanding on the actual
> needs. In the end the driver is in staging, and the potential for errors
> small.
>
> Regards,
> Nicolas
>
> [1] https://github.com/raspberrypi/linux/issues/2881
>
[1] - https://archlinuxarm.org/forum/viewtopic.php?f=65&t=13485

[2] -
https://lists.fedoraproject.org/archives/list/arm@lists.fedoraproject.org/message/GBXGJ7DOV5CQQXFPOZCXTRD6W4BEPT4Q/