On Wed, Sep 03, 2014 at 06:08:19PM +0200, 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?
Looking at 82727018b it appears the intent was to make sure we don't re-create ->numa_fault after we free it. But you're right, we should never get there with TASK_DEAD. Also, given that task_numa_free() is called from __put_task_struct() I tihnk we can safely delete this clause. > And a stupid (really, I don't understand this code) question: > > /* for example, ksmd faulting in a user's mm */ > if (!p->mm) > return; In general kernel threads have !->mm, and those cannot do the accounting. The only way to get here is through get_user_pages() with tsk != current and/or mm != current->mm. > 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'm still somewhat fuzzy in the brain but that doesn't appear to actually work, use_mm() explicitly sets ->mm so in that case it would match just fine. That said; I don't think we really need to worry about this. The !->mm case is special in that that cannot ever work, the other cases are extremely rare and will not skew accounting much if anything. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
