Messages in this thread | | | Subject | Re: Multiple oom_reaper BUGs: unmap_page_range racing with exit_mmap | From | Tetsuo Handa <> | Date | Thu, 7 Dec 2017 20:00:58 +0900 |
| |
Michal Hocko wrote: > Hmm, so you are creating a separate process (from the signal point of > view) and I suspect it is one of those that holds the last reference to > the mm_struct which is released here and it has tsk_oom_victim = F
Right.
> So we need a more robust test for the oom victim. Your suggestion is > basically what I came up with originally [1] and which was deemed > ineffective because we took the mmap_sem even for regular paths and > Kirill was afraid this adds some unnecessary cycles to the exit path > which is quite hot. > > So I guess we have to do something else instead. We have to store the > oom flag to the mm struct as well. Something like the patch below.
Yes, adding a new flag for this purpose will work.
Also, setting MMF_UNSTABLE flag between after sending SIGKILL and before victim->mm becomes NULL and testing MMF_UNSTABLE at exit_mm() should work.
But I prefer simple revert + mmget()/mmput_async() approach at http://lkml.kernel.org/r/201712062037.DAF90168.SVFQOJFMOOtHLF@I-love.SAKURA.ne.jp , for my approach not only saves lines but also fixes unexpected change for nommu at http://lkml.kernel.org/r/201711091949.BDB73475.OSHFOMQtLFOFVJ@I-love.SAKURA.ne.jp . Also, if we replace asynchronous OOM reaping by the OOM reaper kernel thread with synchronous OOM reaping by the OOM killer, we can close MMF_OOM_SKIP race window because it is guaranteed that __oom_reap_task_mm() is called before __mmput() is called.
| |