linux-kernel - Re: [PATCH 2/4] x86/Hyper-V: Free hv_panic

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Date:   Tue, 17 Mar 2020 17:36:00 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     ltykernel@...il.com
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        liuwe@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, x86@...nel.org,
        michael.h.kelley@...rosoft.com,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        vkuznets@...hat.com, Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH 2/4] x86/Hyper-V: Free hv_panic_page when fail to
 register kmsg dump

On Tue, Mar 17, 2020 at 06:25:21AM -0700, ltykernel@...il.com wrote:
> From: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> 
> If fail to register kmsg dump on Hyper-V platform, hv_panic_page
> will not be used anywhere. So free and reset it.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> ---
>  drivers/hv/vmbus_drv.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index b56b9fb9bd90..b043efea092a 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1385,9 +1385,13 @@ static int vmbus_bus_init(void)
>  			hv_panic_page = (void *)hv_alloc_hyperv_zeroed_page();
>  			if (hv_panic_page) {
>  				ret = kmsg_dump_register(&hv_kmsg_dumper);
> -				if (ret)
> +				if (ret) {
>  					pr_err("Hyper-V: kmsg dump register "
>  						"error 0x%x\n", ret);
> +					hv_free_hyperv_page(
> +					    (unsigned long)hv_panic_page);
> +					hv_panic_page = NULL;
> +				}

While this modification looks correct to me, there is a call to free
hv_panic_page in the err_alloc path. That makes the error handling a bit
confusing here.

I think you can just remove that function call in err_alloc path.

Wei.

>  			} else
>  				pr_err("Hyper-V: panic message page memory "
>  					"allocation failed");
> -- 
> 2.14.5
>