On Wed, 14 Feb 2018 16:06:40 +0100 Michal Hocko <mho...@kernel.org> wrote:
> On Wed 14-02-18 22:17:34, 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. > > map_update_elem does the following. Unless I am missing something and > the callback doesn't call cpu_map_update_elem there then we are in a > non-preemptible context there and GFP_WAIT would blow up. > rcu_read_lock(); > err = map->ops->map_update_elem(map, key, value, attr->flags); > rcu_read_unlock(); Nope - you did miss something ;-) You are looking at the wrong place. Look at /kernel/bpf/syscall.c line 697. vim +697 kernel/bpf/syscall.c [...] } else if (map->map_type == BPF_MAP_TYPE_CPUMAP) { err = map->ops->map_update_elem(map, key, value, attr->flags); goto out; } You missed that map type BPF_MAP_TYPE_CPUMAP is special cased, and is moved outside rcu_read_{lock,unlock} (because it need to create some kthreads). Further more the BPF-verifier disallow BPF programs runtime changing the BPF_MAP_TYPE_CPUMAP. Right now, we disallow almost everything from the bpf-side (even reading the value): vim +2057 kernel/bpf/verifier.c > > Reported-by: syzbot+1a240cdb1f4cc8881...@syzkaller.appspotmail.com > > Fixes: 0bf7800f1799 ("ptr_ring: try vmalloc() when kmalloc() fails") > > Cc: Michal Hocko <mho...@kernel.org> > > Cc: Daniel Borkmann <dan...@iogearbox.net> > > Cc: Matthew Wilcox <wi...@infradead.org> > > Cc: Jesper Dangaard Brouer <bro...@redhat.com> > > Cc: a...@linux-foundation.org > > Cc: dhowe...@redhat.com > > Cc: han...@cmpxchg.org > > Signed-off-by: Jason Wang <jasow...@redhat.com> > > --- > > 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 > -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer