On 2021/7/30 14:44, Michal Hocko wrote: > On Thu 29-07-21 20:12:43, Roman Gushchin wrote: >> On Thu, Jul 29, 2021 at 08:57:54PM +0800, Miaohe Lin wrote: >>> rtpn might be NULL in very rare case. We have better to check it before >>> dereferencing it. Since memcg can live with NULL rb_tree_per_node in >>> soft_limit_tree, warn this case and continue. >>> >>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >>> --- >>> mm/memcontrol.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>> index 5b4592d1e0f2..70a32174e7c4 100644 >>> --- a/mm/memcontrol.c >>> +++ b/mm/memcontrol.c >>> @@ -7109,6 +7109,8 @@ static int __init mem_cgroup_init(void) >>> rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, >>> node_online(node) ? node : NUMA_NO_NODE); >>> >>> + if (WARN_ON_ONCE(!rtpn)) >>> + continue; >> >> I also really doubt that it makes any sense to continue in this case. >> If this allocations fails (at the very beginning of the system's life, it's an __init function), >> something is terribly wrong and panic'ing on a NULL-pointer dereference sounds like >> a perfect choice. > > Moreover this is 24B allocation during early boot. Kernel will OOM and > panic when not being able to find any victim. I do not think we need to Agree with you. But IMO it may not be a good idea to leave the rtpn without NULL check. We should defend it though it could hardly happen. But I'm not insist on this check. I will drop this patch if you insist. Thanks both of you. > do any special handling here. >
