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| author |   Kirill A. Shutemov <kirill.shutemov@linux.intel.com> | 2014-08-06 16:08:05 -0700 |
|---|---|---|
| committer |   Linus Torvalds <torvalds@linux-foundation.org> | 2014-08-06 18:01:22 -0700 |
| commit | aecd6f44266c13b8709245b21ded2d19291ab070 (patch) | |
| tree | 805e451bb46a2d6091db0d9e23c7f11422aa4121 /mm | |
| parent | memcg, vmscan: Fix forced scan of anonymous pages (diff) | |
| download | linux-dev-aecd6f44266c13b8709245b21ded2d19291ab070.tar.xz linux-dev-aecd6f44266c13b8709245b21ded2d19291ab070.zip | |
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>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/memory.c | 21 |
1 files changed, 7 insertions, 14 deletions
diff --git a/mm/memory.c b/mm/memory.c index 4d0a543f3bb3..dc47261c4686 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2768,16 +2768,6 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address, 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 @@ late_initcall(fault_around_debugfs); 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 @@ static void do_fault_around(struct vm_area_struct *vma, unsigned long address, 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 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, * 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)) |