Messages in this thread | | | Subject | Re: can't oom-kill zap the victim's memory? | From | Raymond Jennings <> | Date | Sat, 19 Sep 2015 16:00:29 -0700 |
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On 09/19/15 15:24, Linus Torvalds wrote: > 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?
Potentially stupid question that others may be asking: Is it legal to return EINTR from mmap() to let a SIGKILL from the OOM handler punch the task out of the kernel and back to userspace?
(sorry for the dupe btw, new email client snuck in html and I got bounced)
> 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 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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