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

[Nicholas Piggin]

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.

I already proposed another patch to bring those local tests under
preempt disable but no response yet

https://patchwork.ozlabs.org/patch/811061/

Thanks,
Nick