[PATCH RT v2] x86/mm/pat: disable preemption __split_large_page() after spin_lock()

[Sebastian Andrzej Siewior]

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 __flush_tlb_all().

Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
v1…v2:
        - add comment
        - enable preemption before dropping the spinlock

 arch/x86/mm/pageattr.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -688,11 +688,17 @@ static int
 
        spin_lock(&pgd_lock);
        /*
+        * Keep preemption disabled after __flush_tlb_all() which expects not be
+        * preempted during the flush of the local TLB.
+        */
+       preempt_disable();
+       /*
         * Check for races, another CPU might have split this page
         * up for us already:
         */
        tmp = _lookup_address_cpa(cpa, address, &level);
        if (tmp != kpte) {
+               preempt_enable();
                spin_unlock(&pgd_lock);
                return 1;
        }
@@ -726,6 +732,7 @@ static int
                break;
 
        default:
+               preempt_enable();
                spin_unlock(&pgd_lock);
                return 1;
        }
@@ -764,6 +771,7 @@ static int
         * going on.
         */
        __flush_tlb_all();
+       preempt_enable();
        spin_unlock(&pgd_lock);
 
        return 0;