mm: unmap VM_PFNMAP mappings with optimized path

When unmapping VM_PFNMAP mappings, vm flags need to be updated. Since the vmas have been detached, so it sounds safe to update vm flags with read mmap_sem. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Yang Shi <[email protected]> Reviewed-by: Matthew Wilcox <[email protected]> Acked-by: Kirill A. Shutemov <[email protected]> Acked-by: Vlastimil Babka <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Vlastimil Babka <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
fracktal · Oct 26, 2018 · cb49224 · cb49224
1 parent b4cefb3
commit cb49224
Showing 1 changed file with 0 additions and 9 deletions.
diff --git a/mm/mmap.c b/mm/mmap.c
@@ -2771,15 +2771,6 @@ static int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 				munlock_vma_pages_all(tmp);
 			}
 
-			/*
-			 * Unmapping vmas, which have VM_HUGETLB or VM_PFNMAP,
-			 * need get done with write mmap_sem held since they may
-			 * update vm_flags.
-			 */
-			if (downgrade &&
-			    (tmp->vm_flags & VM_PFNMAP))
-				downgrade = false;
-
 			tmp = tmp->vm_next;
 		}
 	}