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Commit 701dfbc1 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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[PATCH] mm: mremap correct rmap accounting 



Nick Piggin points out that page accounting on MIPS multiple ZERO_PAGEs
is not maintained by its move_pte, and could lead to freeing a ZERO_PAGE.

Instead of complicating that move_pte, just forget the minor optimization
when mremapping, and change the one thing which needed it for correctness
- filemap_xip use ZERO_PAGE(0) throughout instead of according to address.

[ "There is no block device driver one could use for XIP on mips
   platforms" - Carsten Otte ]

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8339f000

include/asm-mips/pgtable.h

+0 −10
Original line number Diff line number Diff line
@@ -69,16 +69,6 @@ extern unsigned long zero_page_mask; 
#define ZERO_PAGE(vaddr) \

	(virt_to_page((void *)(empty_zero_page + (((unsigned long)(vaddr)) & zero_page_mask))))



#define __HAVE_ARCH_MOVE_PTE

#define move_pte(pte, prot, old_addr, new_addr)				\

({									\

 	pte_t newpte = (pte);						\

	if (pte_present(pte) && pfn_valid(pte_pfn(pte)) &&		\

			pte_page(pte) == ZERO_PAGE(old_addr))		\

		newpte = mk_pte(ZERO_PAGE(new_addr), (prot));		\

	newpte;								\

})



extern void paging_init(void);



/*

mm/filemap_xip.c

+2 −2
Original line number Diff line number Diff line
@@ -183,7 +183,7 @@ __xip_unmap (struct address_space * mapping, 
		address = vma->vm_start +

			((pgoff - vma->vm_pgoff) << PAGE_SHIFT);

		BUG_ON(address < vma->vm_start || address >= vma->vm_end);

		page = ZERO_PAGE(address);

		page = ZERO_PAGE(0);

		pte = page_check_address(page, mm, address, &ptl);

		if (pte) {

			/* Nuke the page table entry. */
@@ -246,7 +246,7 @@ xip_file_nopage(struct vm_area_struct * area, 
		__xip_unmap(mapping, pgoff);

	} else {

		/* not shared and writable, use ZERO_PAGE() */

		page = ZERO_PAGE(address);

		page = ZERO_PAGE(0);

	}



out:

mm/mremap.c

+0 −1
Original line number Diff line number Diff line
@@ -105,7 +105,6 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, 
		if (pte_none(*old_pte))

			continue;

		pte = ptep_clear_flush(vma, old_addr, old_pte);

		/* ZERO_PAGE can be dependant on virtual addr */

		pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);

		set_pte_at(mm, new_addr, new_pte, pte);

	}