[PATCH v3] lockdep: check that no locks held at freeze time

[Mandeep Singh Baines]

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".

Changes since v1:
* LKML: <20130215111635.GA26955@xxxxxxxxx> Ingo Molnar
  * Added a msg string that gets passed in.
* LKML: <20130215154449.GD30829@xxxxxxxxxx> Oleg Nesterov
  * Check PF_NOFREEZE in try_to_freeze().
Changes since v2:
* LKML: <20130216170605.GC4910@xxxxxxxxxx> Oleg Nesterov
  * Avoid unnecessary PF_NOFREEZE check when !CONFIG_LOCKDEP.
* Mandeep Singh Baines
  * Generalize an exit specific printk.

Signed-off-by: Mandeep Singh Baines <msb@xxxxxxxxxxxx>
CC: Oleg Nesterov <oleg@xxxxxxxxxx>
CC: Tejun Heo <tj@xxxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: Rafael J. Wysocki <rjw@xxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
---
 include/linux/debug_locks.h |  5 +++--
 include/linux/freezer.h     |  4 ++++
 kernel/exit.c               |  2 +-
 kernel/lockdep.c            | 10 +++++-----
 4 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/include/linux/debug_locks.h b/include/linux/debug_locks.h
index 3bd46f7..e6c3c85 100644
--- a/include/linux/debug_locks.h
+++ b/include/linux/debug_locks.h
@@ -51,7 +51,8 @@ struct task_struct;
 extern void debug_show_all_locks(void);
 extern void debug_show_held_locks(struct task_struct *task);
 extern void debug_check_no_locks_freed(const void *from, unsigned long len);
-extern void debug_check_no_locks_held(struct task_struct *task);
+extern void debug_check_no_locks_held(struct task_struct *task,
+				      const char *msg);
 #else
 static inline void debug_show_all_locks(void)
 {
@@ -67,7 +68,7 @@ debug_check_no_locks_freed(const void *from, unsigned long len)
 }
 
 static inline void
-debug_check_no_locks_held(struct task_struct *task)
+debug_check_no_locks_held(struct task_struct *task, const char *msg)
 {
 }
 #endif
diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index e4238ce..27ea080 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 +44,9 @@ extern void thaw_kernel_threads(void);
 
 static inline bool try_to_freeze(void)
 {
+	if (!(current->flags & PF_NOFREEZE))
+		debug_check_no_locks_held(current,
+					  "lock held while trying to freeze");
 	might_sleep();
 	if (likely(!freezing(current)))
 		return false;
diff --git a/kernel/exit.c b/kernel/exit.c
index b4df219..88a706c 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -833,7 +833,7 @@ void do_exit(long code)
 	/*
 	 * Make sure we are holding no locks:
 	 */
-	debug_check_no_locks_held(tsk);
+	debug_check_no_locks_held(tsk, "lock held at task exit time");
 	/*
 	 * We can do this unlocked here. The futex code uses this flag
 	 * just to verify whether the pi state cleanup has been done
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 7981e5b..f257b6d 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -4083,7 +4083,7 @@ void debug_check_no_locks_freed(const void *mem_from, unsigned long mem_len)
 }
 EXPORT_SYMBOL_GPL(debug_check_no_locks_freed);
 
-static void print_held_locks_bug(struct task_struct *curr)
+static void print_held_locks_bug(struct task_struct *curr, const char *msg)
 {
 	if (!debug_locks_off())
 		return;
@@ -4092,10 +4092,10 @@ static void print_held_locks_bug(struct task_struct *curr)
 
 	printk("\n");
 	printk("=====================================\n");
-	printk("[ BUG: lock held at task exit time! ]\n");
+	printk("[ BUG: %s! ]\n", msg);
 	print_kernel_ident();
 	printk("-------------------------------------\n");
-	printk("%s/%d is exiting with locks still held!\n",
+	printk("%s/%d still has locks held!\n",
 		curr->comm, task_pid_nr(curr));
 	lockdep_print_held_locks(curr);
 
@@ -4103,10 +4103,10 @@ static void print_held_locks_bug(struct task_struct *curr)
 	dump_stack();
 }
 
-void debug_check_no_locks_held(struct task_struct *task)
+void debug_check_no_locks_held(struct task_struct *task, const char *msg)
 {
 	if (unlikely(task->lockdep_depth > 0))
-		print_held_locks_bug(task);
+		print_held_locks_bug(task, msg);
 }
 
 void debug_show_all_locks(void)
-- 
1.7.12.4

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