On 2023/6/15 16:26, Michal Hocko wrote: > On Thu 15-06-23 07:32:26, Haifeng Xu wrote: >> If mem_cgroup_init() fails to allocate mem_cgroup_tree_per_node, we >> should not try to initilaize it. Add check for this case to avoid >> potential NULL pointer dereference. > > Technically yes and it seems that all users of soft_limit_tree.rb_tree_per_node > correctly check for NULL so this would be graceful failure handling. At > least superficially because the feature itself would be semi-broken when > used. But more practically this is a 24B allocation and if we fail to > allocate that early during the boot we are screwed anyway. Would such > a system have any chance to boot all the way to userspace? Woul any > userspace actually work? > The memory request is too small and It's unlikely to fail during early init. If it fails, I think the system won't work. > Is this patch motivated by a code reading or is there any actual > practical upside of handling the error here? > There is no real world problem, just from code review. >> Signed-off-by: Haifeng Xu <haifeng.xu@xxxxxxxxxx> >> --- >> mm/memcontrol.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index c73c5fb33f65..7ebf64e48b25 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -7422,6 +7422,8 @@ static int __init mem_cgroup_init(void) >> struct mem_cgroup_tree_per_node *rtpn; >> >> rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, node); >> + if (!rtpn) >> + continue; >> >> rtpn->rb_root = RB_ROOT; >> rtpn->rb_rightmost = NULL; >> -- >> 2.25.1 >
