From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 11 Mar 2013 17:09:55 +0100
Subject: x86/highmem: Add a "already used pte" check
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: de2c09025c0225d953d09ec4d3c7f1de427195c1
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

This is a copy from kmap_atomic_prot().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 arch/x86/mm/iomap_32.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/x86/mm/iomap_32.c
+++ b/arch/x86/mm/iomap_32.c
@@ -66,6 +66,8 @@ void *kmap_atomic_prot_pfn(unsigned long
 	type = kmap_atomic_idx_push();
 	idx = type + KM_TYPE_NR * smp_processor_id();
 	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
+	WARN_ON(!pte_none(*(kmap_pte - idx)));
+
 #ifdef CONFIG_PREEMPT_RT_FULL
 	current->kmap_pte[type] = pte;
 #endif