Commit 72866f6f authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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[PATCH] 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: default avatarHugh Dickins <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 6237bcd9
......@@ -1768,13 +1768,14 @@ do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
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. */
......@@ -398,10 +398,9 @@ void free_swap_and_cache(swp_entry_t entry)
* 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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