On Thu, Jan 14, 2016 at 10:11:09PM +0200, Grygorii Strashko wrote:

quoted

diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index deabc36..b9b4f9c 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c

@@ -167,7 +167,7 @@ void switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p)
          * Clear @prev's kmap_atomic mappings
          */
         for (i = 0; i < prev_p->kmap_idx; i++) {
-               int idx = i + KM_TYPE_NR * smp_processor_id();
+               int idx = FIX_KMAP_BEGIN + i + KM_TYPE_NR * smp_processor_id();
  
                 set_fixmap_pte(idx, __pte(0));
         }

@@ -175,7 +175,7 @@ void switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p)
          * Restore @next_p's kmap_atomic mappings
          */
         for (i = 0; i < next_p->kmap_idx; i++) {
-               int idx = i + KM_TYPE_NR * smp_processor_id();
+               int idx = FIX_KMAP_BEGIN + i + KM_TYPE_NR * smp_processor_id();
  
                 if (!pte_none(next_p->kmap_pte[i]))
                         set_fixmap_pte(idx, next_p->kmap_pte[i]);

This looks like it introduces the 4th and 5th copies of the same
calcuation, so can I suggest that we do this to prevent this kind
of error?

diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index d02f8187b1cc..61f0d5941116 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c

@@ -34,6 +34,11 @@ static inline pte_t get_fixmap_pte(unsigned long vaddr)
  	return *ptep;
  }
  
+static unsigned int fixmap_idx(int type)
+{
+	return FIX_KMAP_BEGIN + type + KM_TYPE_NR * smp_processor_id();
+}
+