linux-kernel - Re: [PATCH] hv: Fix unnecessary sleeping in hv_synic

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Message-ID: <87r2rs76wr.fsf@vitty.brq.redhat.com>
Date:   Mon, 18 Dec 2017 09:54:28 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        devel@...uxdriverproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hv: Fix unnecessary sleeping in hv_synic_alloc

Jia-Ju Bai <baijiaju1990@...il.com> writes:

> The kzalloc function is called with GFP_ATOMIC.
> But according to driver call graph, it is not in atomic context,
> namely no spinlock is held nor in an interrupt handler.
>
> This GFP_ATOMIC is unnecessary, and replace with GFP_KERNEL.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  drivers/hv/hv.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 8267439..b0d025a 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -150,7 +150,7 @@ int hv_synic_alloc(void)
>  	int cpu;
>
>  	hv_context.hv_numa_map = kzalloc(sizeof(struct cpumask) * nr_node_ids,
> -					 GFP_ATOMIC);
> +					 GFP_KERNEL);
>  	if (hv_context.hv_numa_map == NULL) {
>  		pr_err("Unable to allocate NUMA map\n");
>  		goto err;

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

The subject line is not very accurate: GFP_KERNEL you switch too is the
one supporting 'sleep' when there's not enough memory, not
GFP_ATOMIC so you don't actually "Fix unnecessary sleeping". I'd suggest
you use something like "hyper-v: use GFP_KERNEL for hv_context.hv_numa_map"

-- 
  Vitaly