On 2021/7/30 11:12, 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. > > Is this a real world problem? Do I miss something? No, this is a theoretical bug, a very race case but not impossible IMO. Since we can't live with NULL rb_tree_per_node in soft_limit_tree, I thinks simply continue or break here without panic is also acceptable. Or is it more proper to choose panic here? Thanks. > . >
