Re: WARNING in kvmalloc_node

[Jason Wang]

On 2018å02æ14æ 19:51, Michal Hocko wrote:
> On Wed 14-02-18 19:47:30, Jason Wang wrote:
> > On 2018å02æ14æ 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