Messages in this thread | | | Subject | Re: [PATCH] mm: oom: Fix race condition between oom_badness and do_exit of task | From | "Kohli, Gaurav" <> | Date | Fri, 9 Mar 2018 17:34:39 +0530 |
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On 3/9/2018 4:18 PM, Tetsuo Handa wrote:
> Kohli, Gaurav wrote: >>> t->alloc_lock is still held when leaving find_lock_task_mm(), which means >>> that t->mm != NULL. But nothing prevents t from setting t->mm = NULL at >>> exit_mm() from do_exit() and calling exit_creds() from __put_task_struct(t) >>> after task_unlock(t) is called. Seems difficult to trigger race window. Maybe >>> something has preempted because oom_badness() becomes outside of RCU grace >>> period upon leaving find_lock_task_mm() when called from proc_oom_score(). >> Hi Tetsuo, >> >> Yes it is not easy to reproduce seen twice till now and i agree with >> your analysis. But David has already fixing this in different way, >> So that also looks better to me: >> >> https://patchwork.kernel.org/patch/10265641/ >> > Yes, I'm aware of that patch. > >> But if need to keep that code, So we have to bump up the task >> reference that's only i can think of now. > I don't think so, for I think it is safe to call > has_capability_noaudit(p) with p->alloc_lock held. > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index f2e7dfb..4efcfb8 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -222,7 +222,6 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg, > */ > points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) + > mm_pgtables_bytes(p->mm) / PAGE_SIZE; > - task_unlock(p); > > /* > * Root processes get 3% bonus, just like the __vm_enough_memory() > @@ -230,6 +229,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg, > */ > if (has_capability_noaudit(p, CAP_SYS_ADMIN)) > points -= (points * 3) / 100; > + task_unlock(p);
Earlier i have thought the same to post this, but this may create problem if there are sleeping calls in
has_capability_noaudit ?
> > /* Normalize to oom_score_adj units */ > adj *= totalpages / 1000; > -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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