Re: [PATCH v5] lockdep: check that no locks held at freeze time

[Mandeep Singh Baines]

On Thu, Feb 21, 2013 at 7:42 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> On Wednesday, February 20, 2013 07:17:07 PM Mandeep Singh Baines wrote:
>> We shouldn't try_to_freeze if locks are held.
>
> Has Ingo acked one of the previous versions or is my memory doing tricks?
>

Yes, Ingo had acked a previous version. However, the patch has changed
non-trivially since his ack. I wasn't really sure what do in this
situation. Is it OK to keep the ack?

> Anyway, can you please write something more about what the patch is doing
> in the changelog?  While the statement above is correct, it doesn't really
> explain why it will be a good idea to apply your patch, does it?
>

k, will do

> Rafael
>
>
>> 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 Nesterovw
>>   * Avoid unnecessary PF_NOFREEZE check when !CONFIG_LOCKDEP.
>> * Mandeep Singh Baines
>>   * Generalize an exit specific printk.
>> Changes since v3:
>> * LKML: <20130220223013.GA15760@xxxxxxxxxx> Oleg Nesterovw
>>   * Remove stale vfork comment from commit message.
>> Changes since v4:
>> * LKML: <20130220152446.a65ff84f.akpm@xxxxxxxxxxxxxxxxxxxx> Andrew Morton
>>   * Remove tsk param since tsk is always current.
>>   * Remove msg param, dump_stack() should tell us all we need to know.
>>
>> Signed-off-by: Mandeep Singh Baines <msb@xxxxxxxxxxxx>
>> CC: Ingo Molnar <mingo@xxxxxxxxxx>
>> CC: Oleg Nesterov <oleg@xxxxxxxxxx>
>> CC: Tejun Heo <tj@xxxxxxxxxx>
>> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> CC: Rafael J. Wysocki <rjw@xxxxxxx>
>> ---
>>  include/linux/debug_locks.h |  4 ++--
>>  include/linux/freezer.h     |  3 +++
>>  kernel/exit.c               |  2 +-
>>  kernel/lockdep.c            | 16 +++++++---------
>>  4 files changed, 13 insertions(+), 12 deletions(-)
>>
>> diff --git a/include/linux/debug_locks.h b/include/linux/debug_locks.h
>> index 3bd46f7..a975de1 100644
>> --- a/include/linux/debug_locks.h
>> +++ b/include/linux/debug_locks.h
>> @@ -51,7 +51,7 @@ 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(void);
>>  #else
>>  static inline void debug_show_all_locks(void)
>>  {
>> @@ -67,7 +67,7 @@ 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(void)
>>  {
>>  }
>>  #endif
>> diff --git a/include/linux/freezer.h b/include/linux/freezer.h
>> index e4238ce..c5bd118 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 +44,8 @@ extern void thaw_kernel_threads(void);
>>
>>  static inline bool try_to_freeze(void)
>>  {
>> +     if (!(current->flags & PF_NOFREEZE))
>> +             debug_check_no_locks_held();
>>       might_sleep();
>>       if (likely(!freezing(current)))
>>               return false;
>> diff --git a/kernel/exit.c b/kernel/exit.c
>> index b4df219..aff5bdb 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();
>>       /*
>>        * 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..8e28f56 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(void)
>>  {
>>       if (!debug_locks_off())
>>               return;
>> @@ -4092,21 +4092,19 @@ 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/%d still has locks held! ]\n",
>> +            current->comm, task_pid_nr(current));
>>       print_kernel_ident();
>>       printk("-------------------------------------\n");
>> -     printk("%s/%d is exiting with locks still held!\n",
>> -             curr->comm, task_pid_nr(curr));
>> -     lockdep_print_held_locks(curr);
>> -
>> +     lockdep_print_held_locks(current);
>>       printk("\nstack backtrace:\n");
>>       dump_stack();
>>  }
>>
>> -void debug_check_no_locks_held(struct task_struct *task)
>> +void debug_check_no_locks_held(void)
>>  {
>> -     if (unlikely(task->lockdep_depth > 0))
>> -             print_held_locks_bug(task);
>> +     if (unlikely(current->lockdep_depth > 0))
>> +             print_held_locks_bug();
>>  }
>>
>>  void debug_show_all_locks(void)
>>
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
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