[PATCH] dbg: inject nosplit

[Huang Ying]

---
 mm/migrate.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index 571d8c9fd5bc..d4ee76c285b2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -57,6 +57,11 @@
 
 #include "internal.h"
 
+static noinline bool error_inject_nosplit(void)
+{
+	return false;
+}
+
 int isolate_movable_page(struct page *page, isolate_mode_t mode)
 {
 	const struct movable_operations *mops;
@@ -1412,6 +1417,9 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 	bool nosplit = (reason == MR_NUMA_MISPLACED);
 	bool no_subpage_counting = false;
 
+	if (error_inject_nosplit())
+		nosplit = true;
+
 	trace_mm_migrate_pages_start(mode, reason);
 
 thp_subpage_migration:
-- 
2.35.1
----------------------------------------------------------

With the help of the above patch, the following bpftrace script can
inject the expected error,

--------------------ENOMEM THP + nosplit---------
kprobe:migrate_pages { @in_migrate_pages++; }
kretprobe:migrate_pages  { @in_migrate_pages--; }
kprobe:should_fail_alloc_page / @in_migrate_pages > 0 && arg1 == 9 / {
	override(1);
}
kprobe:error_inject_nosplit / @in_migrate_pages > 0 / {
	override(1);
}
-------------------------------------------------

Although some hack patches are needed.  This is still simpler than my
original hand-made error injection solution.  So I will recommend
developers to use it in the error path testing in the future.

Best Regards,
Huang, Ying