netdev - Re: [PATCH net] bpf: cpumap: use GFP_KERNEL instead of GFP_ATOMIC in __cpu_map_entry

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Date:   Wed, 14 Feb 2018 18:45:32 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     ast@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        akpm@...ux-foundation.org, dhowells@...hat.com, hannes@...xchg.org
Subject: Re: [PATCH net] bpf: cpumap: use GFP_KERNEL instead of GFP_ATOMIC in
 __cpu_map_entry_alloc()

On 02/14/2018 06:04 PM, Michael S. Tsirkin wrote:
> On Wed, Feb 14, 2018 at 10:17:34PM +0800, Jason Wang 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@...kaller.appspotmail.com
>> Fixes: 0bf7800f1799 ("ptr_ring: try vmalloc() when kmalloc() fails")
>> Cc: Michal Hocko <mhocko@...nel.org>
>> Cc: Daniel Borkmann <daniel@...earbox.net>
>> Cc: Matthew Wilcox <willy@...radead.org>
>> Cc: Jesper Dangaard Brouer <brouer@...hat.com>
>> Cc: akpm@...ux-foundation.org
>> Cc: dhowells@...hat.com
>> Cc: hannes@...xchg.org
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
> 
> Frankly I'd start with the revert. The original patch was rushed
> into net without enough justification IMHO, and we just seem to keep
> piling up these things. How about deferring all these ideas
> to net-next?

It's up to you if you think a revert is needed. The below is fine and
small enough in any case for cpumap, imho.

>>  kernel/bpf/cpumap.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> 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;
>>  
>> -- 
>> 2.7.4