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Subject: Re: WARNING in kvmalloc_node
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Daniel Borkmann <daniel@iogearbox.net>,
        Matthew Wilcox <willy@infradead.org>,
        syzbot <syzbot+1a240cdb1f4cc88819df@syzkaller.appspotmail.com>,
        akpm@linux-foundation.org, dhowells@redhat.com, hannes@cmpxchg.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org, mingo@kernel.org,
        rppt@linux.vnet.ibm.com, syzkaller-bugs@googlegroups.com,
        vbabka@suse.cz, viro@zeniv.linux.org.uk,
        Alexei Starovoitov <ast@kernel.org>, netdev@vger.kernel.org,
        brouer@redhat.com, "Michael S. Tsirkin" <mst@redhat.com>
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 <20180214025533.GA28811@bombadil.infradead.org>
 <20180214084308.GX3443@dhcp22.suse.cz>
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 <24351362-a099-3317-2b96-8cdc6835eb1e@redhat.com>
 <20180214115119.GA3443@dhcp22.suse.cz>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <62489a86-b578-b075-3ada-c2f5baf5b787@redhat.com>
Date:   Wed, 14 Feb 2018 20:02:27 +0800
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On 2018年02月14日 19:51, Michal Hocko wrote:
> On Wed 14-02-18 19:47:30, Jason Wang wrote:
>>
>> On 2018年02月14日 17:28, Daniel Borkmann wrote:
>>> [ +Jason, +Jesper ]
>>>
>>> On 02/14/2018 09:43 AM, Michal Hocko wrote:
>>>> On Tue 13-02-18 18:55:33, Matthew Wilcox wrote:
>>>>> On Tue, Feb 13, 2018 at 03:59:01PM -0800, syzbot wrote:
>>>> [...]
>>>>>>    kvmalloc include/linux/mm.h:541 [inline]
>>>>>>    kvmalloc_array include/linux/mm.h:557 [inline]
>>>>>>    __ptr_ring_init_queue_alloc include/linux/ptr_ring.h:474 [inline]
>>>>>>    ptr_ring_init include/linux/ptr_ring.h:492 [inline]
>>>>>>    __cpu_map_entry_alloc kernel/bpf/cpumap.c:359 [inline]
>>>>>>    cpu_map_update_elem+0x3c3/0x8e0 kernel/bpf/cpumap.c:490
>>>>>>    map_update_elem kernel/bpf/syscall.c:698 [inline]
>>>>> Blame the BPF people, not the MM people ;-)
>>> Heh, not really. ;-)
>>>
>>>> Yes. kvmalloc (the vmalloc part) doesn't support GFP_ATOMIC semantic.
>>> Agree, that doesn't work.
>>>
>>> Bug was added in commit 0bf7800f1799 ("ptr_ring: try vmalloc() when kmalloc() fails").
>>>
>>> Jason, please take a look at fixing this, thanks!
>> It looks to me the only solution is to revert that commit.
> Do you really need this to be GFP_ATOMIC? I can see some callers are
> under RCU read lock but can we perhaps do the allocation outside of this
> section?

If I understand the code correctly, the code would be called by XDP 
program (usually run inside a bh) which makes it hard to do this.

Rethink of this, we can probably test gfp and not call kvmalloc if 
GFP_ATOMIC is set in __ptr_ring_init_queue_alloc().

Thanks