On Sat, Jul 14, 2018 at 7:10 PM 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. > Hi Yafang, If you check mem_cgroup_charge_skmem(), the memcg passed is not 'current' but is from the sock object i.e. sk->sk_memcg for which the network buffer is allocated for. If the network buffers is allocated through kmem interface, the charging is bypassed altogether (through memcg_kmem_bypass()) for interrupt context. regards, Shakeel
