[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: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 9dd9fbb..cbb3358 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -17,6 +17,29 @@
#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
* stuff.
@@ -162,7 +185,7 @@
* 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 @@
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 @@
+ 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 @@
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:
