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. Thanks Yafang
