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Commit 72866f6f authored Oct 29, 2005 by Hugh Dickins Committed by Linus Torvalds Oct 29, 2005

[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: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 6237bcd9

mm/memory.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -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. */
		pte_unmap(page_table);
		spin_unlock(&mm->page_table_lock);

mm/swapfile.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -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.
		*/