v1->v2: Add description about the bug potential trigger condition. Thanks for the review/suggestion of Michal Hocko & Wanpeng Li. In collapse_huge_page, there is a race window between release the mmap_sem read lock and hold the mmap_sem write lock, so find_vma() may return NULL, thus check the return value to avoid NULL pointer dereference. collapse_huge_page khugepaged_alloc_page up_read(&mm->mmap_sem) down_write(&mm->mmap_sem) vma = find_vma(mm, address) Signed-off-by: Libin <huawei.libin@xxxxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reviewed-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx> Reviewed-by: Michal Hocko <mhocko@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # v3.0+ --- 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>