[PATCH] powerpc/64s/radix: fix preempt imbalance in TLB flush

[Nicholas Piggin]

On Tue, 10 Oct 2017 19:09:54 +0530
"Aneesh Kumar K.V" <aneeshkumar.opensource at gmail.com> wrote:

> 
> 
> On 10/10/2017 04:02 PM, Nicholas Piggin wrote:
> > On Tue, 10 Oct 2017 15:52:02 +0530
> > "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com> wrote:
> >
> >> On 10/10/2017 03:46 PM, Nicholas Piggin wrote:
> >>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> >>> ---
> >>>    arch/powerpc/mm/tlb-radix.c | 3 ++-
> >>>    1 file changed, 2 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/arch/powerpc/mm/tlb-radix.c b/arch/powerpc/mm/tlb-radix.c
> >>> index b3e849c4886e..de414460287a 100644
> >>> --- a/arch/powerpc/mm/tlb-radix.c
> >>> +++ b/arch/powerpc/mm/tlb-radix.c
> >>> @@ -358,7 +358,7 @@ void radix__flush_tlb_collapsed_pmd(struct mm_struct *mm, unsigned long addr)
> >>>    	unsigned long ap = mmu_get_ap(mmu_virtual_psize);
> >>>    	unsigned long pid, end;
> >>>
> >>> -
> >>> +	preempt_disable();
> >>>    	pid = mm ? mm->context.id : 0;
> >>>    	if (unlikely(pid == MMU_NO_CONTEXT))
> >>>    		goto no_context;
> >>> @@ -366,6 +366,7 @@ void radix__flush_tlb_collapsed_pmd(struct mm_struct *mm, unsigned long addr)
> >>>    	/* 4k page size, just blow the world */
> >>>    	if (PAGE_SIZE == 0x1000) {
> >>>    		radix__flush_all_mm(mm);
> >>> +		preempt_enable();
> >>>    		return;
> >>>    	}
> >>>    
> >> Can't we do a preempt_disable before the if (local) check?. That way we
> >> don't need that prempt_enable in that PAGE_SIZE==0x1000 path.We already
> >> do disable/enable correctly in radix__flush_all_mm(mm)
> > Well this is just to fix the imbalance. Nested preempt doesn't matter
> > much, and these are all no-ops for !preempt kernel, unless you turn on
> > debugging.
> 
> But this patch is still doing the mm_is_thread_local() test outside 
> preempt_disable() right?

Yes. As it does in some other place too. It's just a minimal fix for
the imbalance issue as I said, because that's messing up debugging.

> > I already proposed another patch to bring those local tests under
> > preempt disable but no response yet
> >
> > https://patchwork.ozlabs.org/patch/811061/
> >
> 
> That is a much better patch?

I'm planning to repost the series but have been side-tracked hitting
testing it due to hitting bugs (!preempt though, so this has not been
top priority).

Thanks,
Nick