On 2013/7/24 12:35, Wanpeng Li wrote: > On Wed, Jul 24, 2013 at 12:22:08PM +0800, Wanpeng Li wrote: >> On Wed, Jul 24, 2013 at 11:48:19AM +0800, Libin wrote: >>> find_vma may return NULL, thus check the return >>> value to avoid NULL pointer dereference. >>> >> >> When can this happen since down_read(&mm->mmap_sem) is held? >> > > Between mmap_sem read lock released and write lock held I think. > Yes, In khugepaged_alloc_page mmap_sem read lock was released. Thanks for your reply. Libin. >>> Signed-off-by: Libin <huawei.libin@xxxxxxxxxx> >>> --- >>> mm/huge_memory.c | 2 ++ >>> 1 file changed, 2 insertions(+) >>> >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 243e710..d4423f4 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -2294,6 +2294,8 @@ static void collapse_huge_page(struct mm_struct *mm, >>> goto out; >>> >>> vma = find_vma(mm, address); >>> + if (!vma) >>> + goto out; >>> hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; >>> hend = vma->vm_end & HPAGE_PMD_MASK; >>> if (address < hstart || address + HPAGE_PMD_SIZE > hend) >>> -- >>> 1.8.2.1 >>> >>> >>> -- >>> To unsubscribe, send a message with 'unsubscribe linux-mm' in >>> the body to majordomo@xxxxxxxxx. For more info on Linux MM, >>> see: http://www.linux-mm.org/ . >>> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> >> >> -- >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> the body to majordomo@xxxxxxxxx. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > > > . > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>