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Commit a76c0b97 authored by Carsten Otte's avatar Carsten Otte Committed by Linus Torvalds
Browse files

[PATCH] mm: fix xip issue with /dev/zero 



Fix the bug, that reading into xip mapping from /dev/zero fills the user
page table with ZERO_PAGE() entries.  Later on, xip cannot tell which pages
have been ZERO_PAGE() filled by access to a sparse mapping, and which ones
origin from /dev/zero.  It will unmap ZERO_PAGE from all mappings when
filling the sparse hole with data.  xip does now use its own zeroed page
for its sparse mappings.  Please apply.

Signed-off-by: default avatarCarsten Otte <cotte@de.ibm.com>
Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 90ed52eb

mm/filemap_xip.c

+37 −11
Original line number Diff line number Diff line
@@ -16,6 +16,29 @@ 
#include <asm/tlbflush.h>

#include "filemap.h"



/*

 * We do use our own empty page to avoid interference with other users

 * of ZERO_PAGE(), such as /dev/zero

 */

static struct page *__xip_sparse_page;



static struct page *xip_sparse_page(void)

{

	if (!__xip_sparse_page) {

		unsigned long zeroes = get_zeroed_page(GFP_HIGHUSER);

		if (zeroes) {

			static DEFINE_SPINLOCK(xip_alloc_lock);

			spin_lock(&xip_alloc_lock);

			if (!__xip_sparse_page)

				__xip_sparse_page = virt_to_page(zeroes);

			else

				free_page(zeroes);

			spin_unlock(&xip_alloc_lock);

		}

	}

	return __xip_sparse_page;

}



/*

 * This is a file read routine for execute in place files, and uses

 * the mapping->a_ops->get_xip_page() function for the actual low-level
@@ -162,7 +185,7 @@ EXPORT_SYMBOL_GPL(xip_file_sendfile); 
 * xip_write

 *

 * This function walks all vmas of the address_space and unmaps the

 * ZERO_PAGE when found at pgoff. Should it go in rmap.c?

 * __xip_sparse_page when found at pgoff.

 */

static void

__xip_unmap (struct address_space * mapping,
@@ -177,13 +200,16 @@ __xip_unmap (struct address_space * mapping, 
	spinlock_t *ptl;

	struct page *page;



	page = __xip_sparse_page;

	if (!page)

		return;



	spin_lock(&mapping->i_mmap_lock);

	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {

		mm = vma->vm_mm;

		address = vma->vm_start +

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

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

		page = ZERO_PAGE(0);

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

		if (pte) {

			/* Nuke the page table entry. */
@@ -222,16 +248,14 @@ xip_file_nopage(struct vm_area_struct * area, 
		+ area->vm_pgoff;



	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

	if (pgoff >= size) {

		return NULL;

	}

	if (pgoff >= size)

		return NOPAGE_SIGBUS;



	page = mapping->a_ops->get_xip_page(mapping, pgoff*(PAGE_SIZE/512), 0);

	if (!IS_ERR(page)) {

	if (!IS_ERR(page))

		goto out;

	}

	if (PTR_ERR(page) != -ENODATA)

		return NULL;

		return NOPAGE_SIGBUS;



	/* sparse block */

	if ((area->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
@@ -241,12 +265,14 @@ xip_file_nopage(struct vm_area_struct * area, 
		page = mapping->a_ops->get_xip_page (mapping,

			pgoff*(PAGE_SIZE/512), 1);

		if (IS_ERR(page))

			return NULL;

			return NOPAGE_SIGBUS;

		/* unmap page at pgoff from all other vmas */

		__xip_unmap(mapping, pgoff);

	} else {

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

		page = ZERO_PAGE(0);

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

		page = xip_sparse_page();

		if (!page)

			return NOPAGE_OOM;

	}



out: