Re: WARNING in kvmalloc_node

[Michal Hocko]

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?
-- 
Michal Hocko
SUSE Labs