[PATCH] mm: kmsan: fix instrumentation recursion on preempt_count

[Changbin Du]

This disables msan check for preempt_count_{add,sub} to fix a
instrumentation recursion issue on preempt_count:

  __msan_metadata_ptr_for_load_4() -> kmsan_virt_addr_valid() ->
	preempt_disable() -> __msan_metadata_ptr_for_load_4()

With this fix, I was able to run kmsan kernel with:
  o CONFIG_DEBUG_KMEMLEAK=n
  o CONFIG_KFENCE=n
  o CONFIG_LOCKDEP=n

KMEMLEAK and KFENCE generate too many false positives in unwinding code.
LOCKDEP still introduces instrumenting recursions issue. But these are
other issues expected to be fixed.

Cc: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Changbin Du <changbin.du@xxxxxxxxxx>
---
 kernel/sched/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9116bcc90346..5b63bb98e60a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5848,7 +5848,7 @@ static inline void preempt_latency_start(int val)
 	}
 }
 
-void preempt_count_add(int val)
+void __no_kmsan_checks preempt_count_add(int val)
 {
 #ifdef CONFIG_DEBUG_PREEMPT
 	/*
@@ -5880,7 +5880,7 @@ static inline void preempt_latency_stop(int val)
 		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
 }
 
-void preempt_count_sub(int val)
+void __no_kmsan_checks preempt_count_sub(int val)
 {
 #ifdef CONFIG_DEBUG_PREEMPT
 	/*
-- 
2.25.1