Messages in this thread | | | Date | Wed, 03 Sep 2014 12:33:21 -0400 | From | Rik van Riel <> | Subject | Re: task_numa_fault() && TASK_DEAD |
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On 09/03/2014 12:08 PM, Oleg Nesterov wrote: > On 09/02, Oleg Nesterov wrote: >> >> The usage of TASK_DEAD in task_numa_fault() is wrong in any >> case. > > Rik, I can't understand why task_numa_fault() needs this check at > all, but "if (p->state == TASK_DEAD)" looks certainly wrong. You > could replace this check with BUG_ON(p->state == TASK_DEAD). > Perhaps you meant PF_EXITING?
I do not know why that code is in there, either.
I suspect it was added after some conversation on irc, with either Peter or Mel.
> And a stupid (really, I don't understand this code) question: > > /* for example, ksmd faulting in a user's mm */ if (!p->mm) > return; > > OK, but perhaps it make sense to pass "mm" as another argument and > do > > /* ksmd faulting in a user's mm, or debugger, or kthread use_mm() > caller */ if (p->mm != mm) return;
I suppose that makes sense, since it would be possible for one task to cause a page fault in another task's mm, with eg. ptrace peek/poke or similar code paths.
Currently the numa code could end up accounting such a fault in the wrong mm, when it would be better to not account the fault at all.
This is a bit of a corner case, and probably not the highest priority thing to fix right now, but it would be fairly easy.
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