[PATCH 5.8 440/464] Revert "mm/vmstat.c: do not show lowmem reserve protection information of empty zone"

[Greg Kroah-Hartman]

From: Baoquan He <bhe@xxxxxxxxxx>

commit a8a4b7aeaf841311cb13ff0f6c4710c7a00e68d4 upstream.

This reverts commit 26e7deadaae175.

Sonny reported that one of their tests started failing on the latest
kernel on their Chrome OS platform.  The root cause is that the above
commit removed the protection line of empty zone, while the parser used in
the test relies on the protection line to mark the end of each zone.

Let's revert it to avoid breaking userspace testing or applications.

Fixes: 26e7deadaae175 ("mm/vmstat.c: do not show lowmem reserve protection information of empty zone)"
Reported-by: Sonny Rao <sonnyrao@xxxxxxxxxxxx>
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>	[5.8.x]
Link: http://lkml.kernel.org/r/20200811075412.12872-1-bhe@xxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/vmstat.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1596,12 +1596,6 @@ static void zoneinfo_show_print(struct s
 		   zone->present_pages,
 		   zone_managed_pages(zone));
 
-	/* If unpopulated, no other information is useful */
-	if (!populated_zone(zone)) {
-		seq_putc(m, '\n');
-		return;
-	}
-
 	seq_printf(m,
 		   "\n        protection: (%ld",
 		   zone->lowmem_reserve[0]);
@@ -1609,6 +1603,12 @@ static void zoneinfo_show_print(struct s
 		seq_printf(m, ", %ld", zone->lowmem_reserve[i]);
 	seq_putc(m, ')');
 
+	/* If unpopulated, no other information is useful */
+	if (!populated_zone(zone)) {
+		seq_putc(m, '\n');
+		return;
+	}
+
 	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
 		seq_printf(m, "\n      %-12s %lu", zone_stat_name(i),
 			   zone_page_state(zone, i));