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SubjectRe: PowerPC BUG: using smp_processor_id() in preemptible code
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On Thu, 2011-02-24 at 12:47 -0800, Hugh Dickins wrote:

> Reading back, I see Jeremy suggested moving vb_free()'s call to
> vunmap_page_range() back inside vb->lock: it certainly was his moving
> the call out from under that lock that brought the issue to my notice;
> but it looked as if there were other paths which would give preemptible
> PowerPC the same issue, just paths I happen not to go down myself. I'm
> not sure, I didn't take the time to follow it up properly, expecting
> further insight to arrive shortly from Ben!

Yeah, sorry, I've been too over extended lately...

> And, as threatened, Jeremy has further vmalloc changes queued up in
> mmotm, which certainly make the patch below inadequate, and I imagine
> the vunmap_page_range() movement too. I'm currently (well, I think most
> recent mmotm doesn't even boot on my ppc) having to disable preemption
> in the kernel case of apply_to_pte_range().
>
> What would be better for 2.6.38 and 2.6.37-stable? Moving that call to
> vunmap_page_range back under vb->lock, or the partial-Peter-patch below?
> And then what should be done for 2.6.39?

Patch is fine. I should send it to Linus. It's not like we have a batch
on the vmalloc space anyways since it doesnt do the arch_lazy_mmu stuff,
so it's really about protecting the per-cpu variable.

Cheers,
Ben.

> --- 2.6.38-rc5/arch/powerpc/mm/tlb_hash64.c 2010-02-24 10:52:17.000000000 -0800
> +++ linux/arch/powerpc/mm/tlb_hash64.c 2011-02-15 23:27:21.000000000 -0800
> @@ -38,13 +38,11 @@ DEFINE_PER_CPU(struct ppc64_tlb_batch, p
> * neesd to be flushed. This function will either perform the flush
> * immediately or will batch it up if the current CPU has an active
> * batch on it.
> - *
> - * Must be called from within some kind of spinlock/non-preempt region...
> */
> void hpte_need_flush(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep, unsigned long pte, int huge)
> {
> - struct ppc64_tlb_batch *batch = &__get_cpu_var(ppc64_tlb_batch);
> + struct ppc64_tlb_batch *batch = &get_cpu_var(ppc64_tlb_batch);
> unsigned long vsid, vaddr;
> unsigned int psize;
> int ssize;
> @@ -99,6 +97,7 @@ void hpte_need_flush(struct mm_struct *m
> */
> if (!batch->active) {
> flush_hash_page(vaddr, rpte, psize, ssize, 0);
> + put_cpu_var(ppc64_tlb_batch);
> return;
> }
>
> @@ -127,6 +126,7 @@ void hpte_need_flush(struct mm_struct *m
> batch->index = ++i;
> if (i >= PPC64_TLB_BATCH_NR)
> __flush_tlb_pending(batch);
> + put_cpu_var(ppc64_tlb_batch);
> }
>
> /*
> --
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