Rework ptep_set_access_flags and fix sun4c

Some changes done a while ago to avoid pounding on ptep_set_access_flags and
update_mmu_cache in some race situations break sun4c which requires
update_mmu_cache() to always be called on minor faults.

This patch reworks ptep_set_access_flags() semantics, implementations and
callers so that it's now responsible for returning whether an update is
necessary or not (basically whether the PTE actually changed).  This allow
fixing the sparc implementation to always return 1 on sun4c.

[akpm@linux-foundation.org: fixes, cleanups]
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: David Miller <davem@davemloft.net>
Cc: Mark Fortescue <mark@mtfhpc.demon.co.uk>
Acked-by: William Lee Irwin III <wli@holomorphy.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 7 deletions

diff --git a/mm/memory.c b/mm/memory.c
index cb94488ab96..f64cbf9baa3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1691,9 +1691,10 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 flush_cache_page(vma, address, pte_pfn(orig_pte));
                 entry = pte_mkyoung(orig_pte);
                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
-                ptep_set_access_flags(vma, address, page_table, entry, 1);
-                update_mmu_cache(vma, address, entry);
-                lazy_mmu_prot_update(entry);
+                if (ptep_set_access_flags(vma, address, page_table, entry,1)) {
+                        update_mmu_cache(vma, address, entry);
+                        lazy_mmu_prot_update(entry);
+                }
                 ret |= VM_FAULT_WRITE;
                 goto unlock;
         }
@@ -2525,10 +2526,9 @@ static inline int handle_pte_fault(struct mm_struct *mm,
                 pte_t *pte, pmd_t *pmd, int write_access)
 {
         pte_t entry;
-        pte_t old_entry;
         spinlock_t *ptl;
 
-        old_entry = entry = *pte;
+        entry = *pte;
         if (!pte_present(entry)) {
                 if (pte_none(entry)) {
                         if (vma->vm_ops) {
@@ -2561,8 +2561,7 @@ static inline int handle_pte_fault(struct mm_struct *mm,
                 entry = pte_mkdirty(entry);
         }
         entry = pte_mkyoung(entry);
-        if (!pte_same(old_entry, entry)) {
-                ptep_set_access_flags(vma, address, pte, entry, write_access);
+        if (ptep_set_access_flags(vma, address, pte, entry, write_access)) {
                 update_mmu_cache(vma, address, entry);
                 lazy_mmu_prot_update(entry);
         } else {