[PATCH v3] mm/msync: exit early when the flags is an MS_ASYNC and start < vm_start

[Nikita Ermakov <sh1r4s3@mail.si-head.nl>]

If an unmapped region was found and the flag is MS_ASYNC (without
MS_INVALIDATE) there is nothing to do and the result would be always
-ENOMEM, so return immediately.

Signed-off-by: Nikita Ermakov <sh1r4s3@mail.si-head.nl>
---
 mm/msync.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/msync.c b/mm/msync.c
index 69c6d2029531..137d1c104f3e 100644
--- a/mm/msync.c
+++ b/mm/msync.c
@@ -55,7 +55,9 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
 		goto out;
 	/*
 	 * If the interval [start,end) covers some unmapped address ranges,
-	 * just ignore them, but return -ENOMEM at the end.
+	 * just ignore them, but return -ENOMEM at the end. Besides, if the
+	 * flag is MS_ASYNC (w/o MS_INVALIDATE) the result would be -ENOMEM
+	 * anyway and there is nothing left to do, so return immediately.
 	 */
 	mmap_read_lock(mm);
 	vma = find_vma(mm, start);
@@ -69,6 +71,8 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, len, int, flags)
 			goto out_unlock;
 		/* Here start < vma->vm_end. */
 		if (start < vma->vm_start) {
+			if (flags == MS_ASYNC)
+				goto out_unlock;
 			start = vma->vm_start;
 			if (start >= end)
 				goto out_unlock;

base-commit: 6824a8a9b4861d7df7ee132a952bdf6f84a99cb8
-- 
2.28.0