On Thu, 13 Dec 2018 17:44:31 +0100
Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:
> Commit "x86/mm/pat: Disable preemption around __flush_tlb_all()" added a
> warning if __flush_tlb_all() is invoked in preemptible context. On !RT
> the warning does not trigger because a spin lock is acquired which
> disables preemption. On RT the spin lock does not disable preemption and
> so the warning is seen.
>
> Disable preemption to avoid the warning in __flush_tlb_all().
I'm guessing the reason for the warn on is that we don't want a task to
be scheduled in where we expected the TLB to have been flushed.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> arch/x86/mm/pageattr.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index e2d4b25c7aa44..abbe3e93ec266 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -687,6 +687,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
> pgprot_t ref_prot;
>
> spin_lock(&pgd_lock);
We probably should have comment explaining why we have a
preempt_disable here.
> + preempt_disable();
> /*
> * Check for races, another CPU might have split this page
> * up for us already:
> @@ -694,6 +695,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
> tmp = _lookup_address_cpa(cpa, address, &level);
> if (tmp != kpte) {
> spin_unlock(&pgd_lock);
> + preempt_enable();
Shouldn't the preempt_enable() be before the unlock?
> return 1;
> }
>
> @@ -727,6 +729,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
>
> default:
> spin_unlock(&pgd_lock);
> + preempt_enable();
Here too.
-- Steve
> return 1;
> }
>
> @@ -764,6 +767,7 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
> * going on.
> */
> __flush_tlb_all();
> + preempt_enable();
> spin_unlock(&pgd_lock);
>
> return 0;
