[PATCH 3/4] mm/madvise: deduplicate madvise_do_behavior() skip case handlings

[SeongJae Park <sj@kernel.org>]

The logic for checking if a given madvise() request for a single memory
range can skip real work, namely madvise_do_behavior(), is duplicated in
do_madvise() and vector_madvise().  Split out the logic to a function
and reuse it.

Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 mm/madvise.c | 57 +++++++++++++++++++++++++++++++---------------------
 1 file changed, 34 insertions(+), 23 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 611db868ae38..ba006d05c7ea 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1640,6 +1640,31 @@ static bool is_valid_madvise(unsigned long start, size_t len_in, int behavior)
 	return true;
 }
 
+/*
+ * madvise_should_skip() - Return if the request is invalid or nothing.
+ * @start:	Start address of madvise-requested address range.
+ * @len_in:	Length of madvise-requested address range.
+ * @behavior:	Requested madvise behavor.
+ * @err:	Pointer to store an error code from the check.
+ *
+ * If the specified behaviour is invalid or nothing would occur, we skip the
+ * operation.  This function returns true in the cases, otherwise false.  In
+ * the former case we store an error on @err.
+ */
+static bool madvise_should_skip(unsigned long start, size_t len_in,
+		int behavior, int *err)
+{
+	if (!is_valid_madvise(start, len_in, behavior)) {
+		*err = -EINVAL;
+		return true;
+	}
+	if (start + PAGE_ALIGN(len_in) == start) {
+		*err = 0;
+		return true;
+	}
+	return false;
+}
+
 static bool is_madvise_populate(int behavior)
 {
 	switch (behavior) {
@@ -1747,23 +1772,15 @@ static int madvise_do_behavior(struct mm_struct *mm,
  */
 int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior)
 {
-	unsigned long end;
 	int error;
-	size_t len;
-
-	if (!is_valid_madvise(start, len_in, behavior))
-		return -EINVAL;
-
-	len = PAGE_ALIGN(len_in);
-	end = start + len;
-
-	if (end == start)
-		return 0;
 
+	if (madvise_should_skip(start, len_in, behavior, &error))
+		return error;
 	error = madvise_lock(mm, behavior);
 	if (error)
 		return error;
-	error = madvise_do_behavior(mm, start, len_in, len, behavior);
+	error = madvise_do_behavior(mm, start, len_in, PAGE_ALIGN(len_in),
+			behavior);
 	madvise_unlock(mm, behavior);
 
 	return error;
@@ -1790,19 +1807,13 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
 	while (iov_iter_count(iter)) {
 		unsigned long start = (unsigned long)iter_iov_addr(iter);
 		size_t len_in = iter_iov_len(iter);
-		size_t len;
-
-		if (!is_valid_madvise(start, len_in, behavior)) {
-			ret = -EINVAL;
-			break;
-		}
+		int error;
 
-		len = PAGE_ALIGN(len_in);
-		if (start + len == start)
-			ret = 0;
+		if (madvise_should_skip(start, len_in, behavior, &error))
+			ret = error;
 		else
-			ret = madvise_do_behavior(mm, start, len_in, len,
-					behavior);
+			ret = madvise_do_behavior(mm, start, len_in,
+					PAGE_ALIGN(len_in), behavior);
 		/*
 		 * An madvise operation is attempting to restart the syscall,
 		 * but we cannot proceed as it would not be correct to repeat
-- 
2.39.5