[PATCH 2/5] lockdep: check that no locks held at freeze time

[Mandeep Singh Baines <msb@chromium.org>]

We shouldn't try_to_freeze if locks are held. Verified that
I get no lockdep warnings after applying this patch and
"vfork: don't freezer_count() for in-kernel users of CLONE_VFORK".

Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Tejun Heo <tj@kernel.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Rafael J. Wysocki <rjw@sisk.pl>
CC: Ingo Molnar <mingo@redhat.com>
---
 include/linux/freezer.h | 2 ++
 kernel/lockdep.c        | 6 +++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index e4238ce..1538cfc 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -3,6 +3,7 @@
 #ifndef FREEZER_H_INCLUDED
 #define FREEZER_H_INCLUDED
 
+#include <linux/debug_locks.h>
 #include <linux/sched.h>
 #include <linux/wait.h>
 #include <linux/atomic.h>
@@ -43,6 +44,7 @@ extern void thaw_kernel_threads(void);
 
 static inline bool try_to_freeze(void)
 {
+	debug_check_no_locks_held(current);
 	might_sleep();
 	if (likely(!freezing(current)))
 		return false;
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 7981e5b..e3ee8af 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -4091,10 +4091,10 @@ static void print_held_locks_bug(struct task_struct *curr)
 		return;
 
 	printk("\n");
-	printk("=====================================\n");
-	printk("[ BUG: lock held at task exit time! ]\n");
+	printk("=======================================\n");
+	printk("[ BUG: lock held at exit/freeze time! ]\n");
 	print_kernel_ident();
-	printk("-------------------------------------\n");
+	printk("---------------------------------------\n");
 	printk("%s/%d is exiting with locks still held!\n",
 		curr->comm, task_pid_nr(curr));
 	lockdep_print_held_locks(curr);
-- 
1.8.1