On Sun, Jul 15, 2018 at 10:10 AM, Yafang Shao <laoar.shao@xxxxxxxxx> wrote: > On Sat, Jul 14, 2018 at 11:38 PM, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote: >> On Sat, Jul 14, 2018 at 1:32 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote: >>> >>> try_charge maybe executed in packet receive path, which is in interrupt >>> context. >>> In this situation, the 'current' is the interrupted task, which may has >>> no relation to the rx softirq, So it is nonsense to use 'current'. >>> >> >> Have you actually seen this occurring? > > Hi Shakeel, > > I'm trying to produce this issue, but haven't find it occur yet. > >> I am not very familiar with the >> network code but I can think of two ways try_charge() can be called >> from network code. Either through kmem charging or through >> mem_cgroup_charge_skmem() and both locations correctly handle >> interrupt context. >> > > Why do you say that mem_cgroup_charge_skmem() correctly hanle > interrupt context ? > > Let me show you why mem_cgroup_charge_skmem isn't hanling interrupt > context correctly. > > mem_cgroup_charge_skmem() is calling try_charge() twice. > The first one is with GFP_NOWAIT as the gfp_mask, and the second one > is with (GFP_NOWAIT | __GFP_NOFAIL) as the gfp_mask. > > If page_counter_try_charge() failes at the first time, -ENOMEM is returned. > Then mem_cgroup_charge_skmem() will call try_charge() once more with > __GFP_NOFAIL set, and this time if If page_counter_try_charge() failes > again the ' > force' label in try_charge() will be executed and 0 is returned. > > No matter what, the 'current' will be used and touched, that is > meaning mem_cgroup_charge_skmem() isn't hanling the interrupt context > correctly. > > Pls. let me know if I miss something. > > Maybe bellow change is better, @@ -2123,6 +2123,9 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, goto retry; } + if (!gfpflags_allow_blocking(gfp_mask)) + goto nomem; + /* * Unlike in global OOM situations, memcg is not in a physical * memory shortage. Allow dying and OOM-killed tasks to @@ -2146,9 +2149,6 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, if (unlikely(task_in_memcg_oom(current))) goto nomem; - if (!gfpflags_allow_blocking(gfp_mask)) - goto nomem; Thanks Yafang