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SubjectRe: WARNING in kvmalloc_node

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().


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