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Date:   Wed, 14 Feb 2018 15:20:20 +0100
From:   Jesper Dangaard Brouer <brouer@redhat.com>
To:     Jason Wang <jasowang@redhat.com>
Cc:     ast@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, mst@redhat.com,
        Michal Hocko <mhocko@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        akpm@linux-foundation.org, dhowells@redhat.com, hannes@cmpxchg.org,
        brouer@redhat.com
Subject: Re: [PATCH net] bpf: cpumap: use GFP_KERNEL instead of GFP_ATOMIC
 in __cpu_map_entry_alloc()
Message-ID: <20180214152020.70985ce3@redhat.com>
In-Reply-To: <1518617854-4486-1-git-send-email-jasowang@redhat.com>
References: <1518617854-4486-1-git-send-email-jasowang@redhat.com>
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On Wed, 14 Feb 2018 22:17:34 +0800
Jason Wang <jasowang@redhat.com> wrote:

> There're several implications after commit 0bf7800f1799 ("ptr_ring:
> try vmalloc() when kmalloc() fails") with the using of vmalloc() since
> can't allow GFP_ATOMIC but mandate GFP_KERNEL. This will lead a WARN
> since cpumap try to call with GFP_ATOMIC. Fortunately, entry
> allocation of cpumap can only be done through syscall path which means
> GFP_ATOMIC is not necessary, so fixing this by replacing GFP_ATOMIC
> with GFP_KERNEL.
> 
> Reported-by: syzbot+1a240cdb1f4cc88819df@syzkaller.appspotmail.com
> Fixes: 0bf7800f1799 ("ptr_ring: try vmalloc() when kmalloc() fails")
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Jesper Dangaard Brouer <brouer@redhat.com>
> Cc: akpm@linux-foundation.org
> Cc: dhowells@redhat.com
> Cc: hannes@cmpxchg.org
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  kernel/bpf/cpumap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>


> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index fbfdada6..a4bb0b3 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -334,7 +334,7 @@ static int cpu_map_kthread_run(void *data)
>  static struct bpf_cpu_map_entry *__cpu_map_entry_alloc(u32 qsize, u32 cpu,
>  						       int map_id)
>  {
> -	gfp_t gfp = GFP_ATOMIC|__GFP_NOWARN;
> +	gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
>  	struct bpf_cpu_map_entry *rcpu;
>  	int numa, err;
>  

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer