[PATCH 4/4] mm/madvise: remove redundant mmap_lock operations from process_madvise()

[SeongJae Park <sj@kernel.org>]

Optimize redundant mmap lock operations from process_madvise() by
directly doing the mmap locking first, and then the remaining works for
all ranges in the loop.

Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/madvise.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 31e5df75b926..5a0a1fc99d27 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1754,9 +1754,26 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
 
 	total_len = iov_iter_count(iter);
 
+	ret = madvise_lock(mm, behavior);
+	if (ret)
+		return ret;
+
 	while (iov_iter_count(iter)) {
-		ret = do_madvise(mm, (unsigned long)iter_iov_addr(iter),
-				 iter_iov_len(iter), behavior);
+		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;
+		}
+
+		len = PAGE_ALIGN(len_in);
+		if (start + len == start)
+			ret = 0;
+		else
+			ret = madvise_do_behavior(mm, start, len_in, len,
+					behavior);
 		/*
 		 * An madvise operation is attempting to restart the syscall,
 		 * but we cannot proceed as it would not be correct to repeat
@@ -1772,12 +1789,17 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
 				ret = -EINTR;
 				break;
 			}
+
+			/* Drop and reacquire lock to unwind race. */
+			madvise_unlock(mm, behavior);
+			madvise_lock(mm, behavior);
 			continue;
 		}
 		if (ret < 0)
 			break;
 		iov_iter_advance(iter, iter_iov_len(iter));
 	}
+	madvise_unlock(mm, behavior);
 
 	ret = (total_len - iov_iter_count(iter)) ? : ret;
 
-- 
2.39.5