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Subject[PATCH 05/21] mm: anon is already wrprotected
do_anonymous_page's pte_wrprotect causes some confusion: in such a case,
vm_page_prot must already be forcing COW, so must omit write permission,
and so the pte_wrprotect is redundant. Replace it by a comment to that
effect, and reword the comment on unuse_pte which also caused confusion.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---
mm/memory.c | 7 ++++---
mm/swapfile.c | 7 +++----
2 files changed, 7 insertions(+), 7 deletions(-)
--- mm04/mm/memory.c 2005-09-24 19:27:05.000000000 +0100
+++ mm05/mm/memory.c 2005-09-24 19:27:19.000000000 +0100
@@ -1768,13 +1768,14 @@ do_anonymous_page(struct mm_struct *mm,
unsigned long addr)
{
pte_t entry;
- struct page * page = ZERO_PAGE(addr);

- /* Read-only mapping of ZERO_PAGE. */
- entry = pte_wrprotect(mk_pte(ZERO_PAGE(addr), vma->vm_page_prot));
+ /* Mapping of ZERO_PAGE - vm_page_prot is readonly */
+ entry = mk_pte(ZERO_PAGE(addr), vma->vm_page_prot);

/* ..except if it's a write access */
if (write_access) {
+ struct page *page;
+
/* Allocate our own private page. */
pte_unmap(page_table);
spin_unlock(&mm->page_table_lock);
--- mm04/mm/swapfile.c 2005-09-22 12:32:04.000000000 +0100
+++ mm05/mm/swapfile.c 2005-09-24 19:27:19.000000000 +0100
@@ -396,10 +396,9 @@ void free_swap_and_cache(swp_entry_t ent
}

/*
- * Always set the resulting pte to be nowrite (the same as COW pages
- * after one process has exited). We don't know just how many PTEs will
- * share this swap entry, so be cautious and let do_wp_page work out
- * what to do if a write is requested later.
+ * No need to decide whether this PTE shares the swap entry with others,
+ * just let do_wp_page work it out if a write is requested later - to
+ * force COW, vm_page_prot omits write permission from any private vma.
*
* vma->vm_mm->page_table_lock is held.
*/
-
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