mm/madvise: remove redundant mmap_lock operations from process_madvise()

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.

[akpm@linux-foundation.org: update comment, per Lorenzo]
Link: https://lkml.kernel.org/r/20250206061517.2958-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Liam R. Howlett <howlett@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 25 insertions, 3 deletions

diff --git a/mm/madvise.c b/mm/madvise.c
index 6e31e3202d71..6ecead476a80 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1778,16 +1778,33 @@ 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
 		 * the operation in aggregate, and would be surprising to the
 		 * user.
 		 *
-		 * As we have already dropped locks, it is safe to just loop and
+		 * We drop and reacquire locks so it is safe to just loop and
 		 * try again. We check for fatal signals in case we need exit
 		 * early anyway.
 		 */
@@ -1796,12 +1813,17 @@ 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;