rds_info_getsockopt() pins the destination user pages with FOLL_WRITE and
the RDS_INFO_* producers memcpy the snapshot into them through
kmap_atomic(). Because that copy goes through the kernel direct map, the
dirty bit on the user PTE is never set, so unpin_user_pages() releases the
pages without marking them dirty. A file-backed destination page can then
be reclaimed without writeback, silently discarding the copied data.

Use unpin_user_pages_dirty_lock() with make_dirty=true so the modified
pages are marked dirty before they are unpinned.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 net/rds/info.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rds/info.c b/net/rds/info.c
index f1b29994934a..17061f6ff74e 100644
--- a/net/rds/info.c
+++ b/net/rds/info.c

@@ -235,7 +235,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
 
 out:
 	if (pages)
-		unpin_user_pages(pages, nr_pages);
+		unpin_user_pages_dirty_lock(pages, nr_pages, true);
 	kfree(pages);
 
 	return ret;

-- 
2.53.0-Meta