Messages in this thread | | | Date | Sat, 19 Sep 2015 15:24:02 -0700 | Subject | Re: can't oom-kill zap the victim's memory? | From | Linus Torvalds <> |
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On Sat, Sep 19, 2015 at 8:03 AM, Oleg Nesterov <oleg@redhat.com> wrote: > + > +static void oom_unmap_func(struct work_struct *work) > +{ > + struct mm_struct *mm = xchg(&oom_unmap_mm, NULL); > + > + if (!atomic_inc_not_zero(&mm->mm_users)) > + return; > + > + // If this is not safe we can do use_mm() + unuse_mm() > + down_read(&mm->mmap_sem);
I don't think this is safe.
What makes you sure that we might not deadlock on the mmap_sem here? For all we know, the process that is going out of memory is in the middle of a mmap(), and already holds the mmap_sem for writing. No?
So at the very least that needs to be a trylock, I think. And I'm not sure zap_page_range() is ok with the mmap_sem only held for reading. Normally our rule is that you can *populate* the page tables concurrently, but you can't tear the down.
Linus
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