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Subject[PATCH v3] lockdep: check that no locks held at freeze time
Date
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@gmail.com> Ingo Molnar
* Added a msg string that gets passed in.
* LKML: <20130215154449.GD30829@redhat.com> Oleg Nesterov
* Check PF_NOFREEZE in try_to_freeze().
Changes since v2:
* LKML: <20130216170605.GC4910@redhat.com> 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@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/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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