netdev - Re: [PATCH] bpf: add schedule points in percpu arrays management

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Date:   Thu, 22 Feb 2018 21:32:50 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>, dennisszhou@...il.com
Subject: Re: [PATCH] bpf: add schedule points in percpu arrays management

[ +Dennis for mm/pcpu ]

On 02/22/2018 05:33 PM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> syszbot managed to trigger RCU detected stalls in
> bpf_array_free_percpu()
> 
> It takes time to allocate a huge percpu map, but even more time to free
> it.
> 
> Since we run in process context, use cond_resched() to yield cpu if
> needed.
> 
> Fixes: a10423b87a7e ("bpf: introduce BPF_MAP_TYPE_PERCPU_ARRAY map")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Applied to bpf tree, thanks Eric!

> ---
>  kernel/bpf/arraymap.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index a364c408f25a54a8175c92b6004a5e7e15f198cb..14750e7c5ee4872e4a7426e960bea7ae001e6623 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -26,8 +26,10 @@ static void bpf_array_free_percpu(struct bpf_array *array)
>  {
>  	int i;
>  
> -	for (i = 0; i < array->map.max_entries; i++)
> +	for (i = 0; i < array->map.max_entries; i++) {
>  		free_percpu(array->pptrs[i]);
> +		cond_resched();
> +	}
>  }
>  
>  static int bpf_array_alloc_percpu(struct bpf_array *array)
> @@ -43,6 +45,7 @@ static int bpf_array_alloc_percpu(struct bpf_array *array)
>  			return -ENOMEM;
>  		}
>  		array->pptrs[i] = ptr;
> +		cond_resched();
>  	}
>  
>  	return 0;
>