linux-kernel - Re: [PATCH V2] x86/Hyper-V: don't allocate clockevent device when synthetic timer is unavailable

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Message-ID: <87sgho22ki.fsf@vitty.brq.redhat.com>
Date:   Tue, 31 Mar 2020 13:20:29 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     ltykernel@...il.com
Cc:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
        kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, michael.h.kelley@...rosoft.com, wei.liu@...nel.org
Subject: Re: [PATCH V2] x86/Hyper-V: don't allocate clockevent device when synthetic timer is unavailable

ltykernel@...il.com writes:

> From: Tianyu Lan <Tianyu.Lan@...rosoft.com>
>
> Current code initializes clock event data structure for syn timer
> even when it's unavailable. Fix it.
>
> Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> ---
> Change since v1:
> 	Update title and commit log. 
>
>  drivers/hv/hv.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 632d25674e7f..2e893768fc76 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -212,13 +212,16 @@ int hv_synic_alloc(void)
>  		tasklet_init(&hv_cpu->msg_dpc,
>  			     vmbus_on_msg_dpc, (unsigned long) hv_cpu);
>  
> -		hv_cpu->clk_evt = kzalloc(sizeof(struct clock_event_device),
> -					  GFP_KERNEL);
> -		if (hv_cpu->clk_evt == NULL) {
> -			pr_err("Unable to allocate clock event device\n");
> -			goto err;
> +		if (ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE) {
> +			hv_cpu->clk_evt =
> +				kzalloc(sizeof(struct clock_event_device),
> +						  GFP_KERNEL);
> +			if (hv_cpu->clk_evt == NULL) {
> +				pr_err("Unable to allocate clock event device\n");
> +				goto err;
> +			}
> +			hv_init_clockevent_device(hv_cpu->clk_evt, cpu);
>  		}
> -		hv_init_clockevent_device(hv_cpu->clk_evt, cpu);
>  
>  		hv_cpu->synic_message_page =
>  			(void *)get_zeroed_page(GFP_ATOMIC);

Thank you for fixing the subject! I had one more question on the
previous version which still stands: which tree is this patch for?
Upstream, clockevent allocation has moved to
drivers/clocksource/hyperv_timer.c and the code there is different.

Is this intended for some stable tree?

-- 
Vitaly