From b179c535a27f0bcefcbfc9f54769703999b2c880 Mon Sep 17 00:00:00 2001
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

This is a copy from kmap_atomic_prot().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

diff --git a/arch/x86/mm/iomap_32.c b/arch/x86/mm/iomap_32.c
index 0c953e3..62377d6 100644
--- a/arch/x86/mm/iomap_32.c
+++ b/arch/x86/mm/iomap_32.c
@@ -65,6 +65,8 @@ void *kmap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
 	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
-- 
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