linux-kernel - Re: [PATCH v2 0/6] arm64: add the time namespace support

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Date:   Sat, 11 Apr 2020 00:33:56 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH v2 0/6] arm64: add the time namespace support

On Thu, Apr 9, 2020 at 6:23 AM Vincenzo Frascino
<vincenzo.frascino@....com> wrote:
>
> Hi Andrei,
>
> On 2/25/20 7:37 AM, Andrei Vagin wrote:
> > Allocate the time namespace page among VVAR pages and add the logic
> > to handle faults on VVAR properly.
> >
> > If a task belongs to a time namespace then the VVAR page which contains
> > the system wide VDSO data is replaced with a namespace specific page
> > which has the same layout as the VVAR page. That page has vdso_data->seq
> > set to 1 to enforce the slow path and vdso_data->clock_mode set to
> > VCLOCK_TIMENS to enforce the time namespace handling path.
> >
> > The extra check in the case that vdso_data->seq is odd, e.g. a concurrent
> > update of the VDSO data is in progress, is not really affecting regular
> > tasks which are not part of a time namespace as the task is spin waiting
> > for the update to finish and vdso_data->seq to become even again.
> >
> > If a time namespace task hits that code path, it invokes the corresponding
> > time getter function which retrieves the real VVAR page, reads host time
> > and then adds the offset for the requested clock which is stored in the
> > special VVAR page.
> >
> > v2: Code cleanups suggested by Vincenzo.
> >
>
> Sorry for the delay, I completed this morning the review of your patches and I
> do not have anymore comments on them. Thank you for making the effort and
> bringing the time namespace support to arm64.

Thank you for the review of these patches.

>
> I have though a question on something I encountered during the testing of the
> patches: I noticed that all the tests related to CLOCK_BOOTTIME_ALARM fail on
> arm64 (please find the results below the scissors). Is this expected?

static int alarm_clock_get_timespec(clockid_t which_clock, struct
timespec64 *tp)
{
        struct alarm_base *base = &alarm_bases[clock2alarm(which_clock)];

        if (!alarmtimer_get_rtcdev())
                return -EINVAL;

It is probably that you get EINVAL from here ^^^. I will send a
separate patch to handle this case in tests properly.

Thanks,
Andrei