mm: close race between do_fault_around() and fault_around_bytes_set()
Things can go wrong if fault_around_bytes will be changed under
do_fault_around(): between fault_around_mask() and fault_around_pages().
Let's read fault_around_bytes only once during do_fault_around() and
calculate mask based on the reading.
Note: fault_around_bytes can only be updated via debug interface. Also
I've tried but was not able to trigger a bad behaviour without the
patch. So I would not consider this patch as urgent.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory.c b/mm/memory.c
index 4d0a543..dc47261 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2768,16 +2768,6 @@
static unsigned long fault_around_bytes = rounddown_pow_of_two(65536);
-static inline unsigned long fault_around_pages(void)
-{
- return fault_around_bytes >> PAGE_SHIFT;
-}
-
-static inline unsigned long fault_around_mask(void)
-{
- return ~(fault_around_bytes - 1) & PAGE_MASK;
-}
-
#ifdef CONFIG_DEBUG_FS
static int fault_around_bytes_get(void *data, u64 *val)
{
@@ -2842,12 +2832,15 @@
static void do_fault_around(struct vm_area_struct *vma, unsigned long address,
pte_t *pte, pgoff_t pgoff, unsigned int flags)
{
- unsigned long start_addr;
+ unsigned long start_addr, nr_pages, mask;
pgoff_t max_pgoff;
struct vm_fault vmf;
int off;
- start_addr = max(address & fault_around_mask(), vma->vm_start);
+ nr_pages = ACCESS_ONCE(fault_around_bytes) >> PAGE_SHIFT;
+ mask = ~(nr_pages * PAGE_SIZE - 1) & PAGE_MASK;
+
+ start_addr = max(address & mask, vma->vm_start);
off = ((address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
pte -= off;
pgoff -= off;
@@ -2859,7 +2852,7 @@
max_pgoff = pgoff - ((start_addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) +
PTRS_PER_PTE - 1;
max_pgoff = min3(max_pgoff, vma_pages(vma) + vma->vm_pgoff - 1,
- pgoff + fault_around_pages() - 1);
+ pgoff + nr_pages - 1);
/* Check if it makes any sense to call ->map_pages */
while (!pte_none(*pte)) {
@@ -2894,7 +2887,7 @@
* something).
*/
if (vma->vm_ops->map_pages && !(flags & FAULT_FLAG_NONLINEAR) &&
- fault_around_pages() > 1) {
+ fault_around_bytes >> PAGE_SHIFT > 1) {
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
do_fault_around(vma, address, pte, pgoff, flags);
if (!pte_same(*pte, orig_pte))