Re: [PATCH v3] kthread: add objectdebug support

[Stephen Boyd <sboyd@kernel.org>]

Quoting Qianli Zhao (2020-08-13 02:55:16)
> From: Qianli Zhao <zhaoqianli@xiaomi.com>
> 
> Add debugobject support to track the life time of kthread_work

Subject says 'objectdebug' but then this says debugobject. Use
debugobject throughout please.

> which is used to detect reinitialization/free active object problems

which is used to detect reinitialization/free active object problems.

> Add kthread_init_work_onstack/kthread_init_delayed_work_onstack for
> kthread onstack support

kthread onstack support.

Also, mark functions with parenthesis please.

> 
> If we reinitialize a kthread_work that has been activated,
> this will cause delayed_work_list/work_list corruption.
> enable this config,there is an chance to fixup these errors

Capitalize enable.

> or WARNING the wrong use of kthread_work
> 
> [30858.395766] list_del corruption. next->prev should be ffffffe388ebbf88, but was ffffffe388ebb588
> [30858.395788] WARNING: CPU: 2 PID: 387 at /home/work/data/codes/build_home/kernel/msm-4.19/lib/list_debug.c:56 __list_del_entry_valid+0xc8/0xd0
> ...
> [30858.405951] list_add corruption. next->prev should be prev (ffffffe389392620), but was ffffffe388ebbf88. (next=ffffffe388ebbf88).
> [30858.405977] WARNING: CPU: 0 PID: 7721 at /home/work/data/codes/build_home/kernel/msm-4.19/lib/list_debug.c:25 __list_add_valid+0x7c/0xc8
> 
> crash> struct kthread_worker.delayed_work_list 0xffffffe3893925f0
>  [ffffffe389392620] delayed_work_list = {
>     next = 0xffffffe388ebbf88,
>     prev = 0xffffffe388ebb588
>   }
> crash> list 0xffffffe388ebbf88
> ffffffe388ebbf88
> 
> Signed-off-by: Qianli Zhao <zhaoqianli@xiaomi.com>
[...]
> diff --git a/include/linux/poison.h b/include/linux/poison.h
> index df34330..2e6a370 100644
> --- a/include/linux/poison.h
> +++ b/include/linux/poison.h
> @@ -86,4 +86,7 @@
>  /********** security/ **********/
>  #define KEY_DESTROY            0xbd
>  
> +/********** kernel/kthread **********/
> +#define KWORK_ENTRY_STATIC     ((void *) 0x600 + POISON_POINTER_DELTA)

Can we get a comment above this like there is for TIMER_ENTRY_STATIC?

> +
>  #endif
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 132f84a..68a16cc 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -67,6 +67,118 @@ enum KTHREAD_BITS {
>         KTHREAD_SHOULD_PARK,
>  };
>  
> +#ifdef CONFIG_DEBUG_OBJECTS_KTHREAD_WORK
> +static struct debug_obj_descr kwork_debug_descr;
> +
> +static void *kwork_debug_hint(void *addr)
> +{
> +       return ((struct kthread_work *) addr)->func;
> +}
> +
> +static bool kwork_is_static_object(void *addr)
> +{
> +       struct kthread_work *kwork = addr;
> +
> +       return (kwork->node.prev == NULL &&
> +               kwork->node.next == KWORK_ENTRY_STATIC);
> +}
> +
> +static bool kwork_fixup_init(void *addr, enum debug_obj_state state)
> +{
> +       struct kthread_work *kwork = addr;
> +
> +       switch (state) {
> +       case ODEBUG_STATE_ACTIVE:
> +               kthread_cancel_work_sync(kwork);
> +               debug_object_init(kwork, &kwork_debug_descr);
> +               return true;
> +       default:
> +               return false;
> +       }
> +}
> +
> +static bool kwork_fixup_free(void *addr, enum debug_obj_state state)
> +{
> +       struct kthread_work *kwork = addr;
> +
> +       switch (state) {
> +       case ODEBUG_STATE_ACTIVE:
> +               kthread_cancel_work_sync(kwork);
> +               debug_object_free(kwork, &kwork_debug_descr);
> +               return true;
> +       default:
> +               return false;
> +       }
> +}
> +
> +static void stub_kthread_work(struct kthread_work *unuse)
> +{
> +       WARN_ON(1);
> +}
> +
> +static bool kwork_fixup_assert_init(void *addr, enum debug_obj_state state)
> +{
> +       struct kthread_work *kwork = addr;
> +       switch (state) {
> +       case ODEBUG_STATE_NOTAVAILABLE:
> +               kthread_init_work(kwork, stub_kthread_work);
> +               return true;
> +       default:
> +               return false;
> +       }
> +}
> +
> +static struct debug_obj_descr kwork_debug_descr = {
> +               .name           = "kthread_work",
> +               .debug_hint     = kwork_debug_hint,
> +               .is_static_object = kwork_is_static_object,
> +               .fixup_init     = kwork_fixup_init,
> +               .fixup_free     = kwork_fixup_free,
> +               .fixup_assert_init = kwork_fixup_assert_init,

Nitpick: This needs some formatting to deindent one tab and align the
equals signs.

> +};
> +
> +static inline void debug_kwork_activate(struct kthread_work *kwork)
> +{
> +       debug_object_activate(kwork, &kwork_debug_descr);
> +}
> +
> +static inline void debug_kwork_deactivate(struct kthread_work *kwork)
> +{
> +       debug_object_deactivate(kwork, &kwork_debug_descr);
> +}
> +
> +static inline void debug_kwork_assert_init(struct kthread_work *kwork)
> +{
> +       debug_object_assert_init(kwork, &kwork_debug_descr);
> +}
> +
> +void __init_kwork(struct kthread_work *kwork, int onstack)
> +{
> +       if (onstack)
> +               debug_object_init_on_stack(kwork, &kwork_debug_descr);
> +       else
> +               debug_object_init(kwork, &kwork_debug_descr);
> +}
> +EXPORT_SYMBOL_GPL(__init_kwork);
> +
> +void destroy_kwork_on_stack(struct kthread_work *kwork)
> +{
> +       debug_object_free(kwork, &kwork_debug_descr);
> +}
> +EXPORT_SYMBOL_GPL(destroy_kwork_on_stack);
> +
> +void destroy_delayed_kwork_on_stack(struct kthread_delayed_work *kdwork)
> +{
> +       destroy_timer_on_stack(&kdwork->timer);
> +       debug_object_free(&kdwork->work, &kwork_debug_descr);
> +}
> +EXPORT_SYMBOL_GPL(destroy_delayed_kwork_on_stack);
> +#else
> +static inline void debug_kwork_activate(struct kthread_work *kwork) { }
> +static inline void debug_kwork_deactivate(struct kthread_work *kwork) { }
> +static inline void debug_kwork_assert_init(struct kthread_work *kwork) { }
> +#endif
> +
>  static inline void set_kthread_struct(void *kthread)
>  {
>         /*
> @@ -697,6 +809,7 @@ int kthread_worker_fn(void *worker_ptr)
>         if (!list_empty(&worker->work_list)) {
>                 work = list_first_entry(&worker->work_list,
>                                         struct kthread_work, node);
> +               debug_kwork_deactivate(work);
>                 list_del_init(&work->node);
>         }
>         worker->current_work = work;
> @@ -833,8 +946,10 @@ static void kthread_insert_work(struct kthread_worker *worker,
>  {
>         kthread_insert_work_sanity_check(worker, work);
>  
> +       debug_kwork_activate(work);
>         list_add_tail(&work->node, pos);
>         work->worker = worker;
> +

Drop this newline.

>         if (!worker->current_work && likely(worker->task))
>                 wake_up_process(worker->task);
>  }
> @@ -857,6 +972,7 @@ bool kthread_queue_work(struct kthread_worker *worker,
>         bool ret = false;
>         unsigned long flags;
>  
> +       debug_kwork_assert_init(work);
>         raw_spin_lock_irqsave(&worker->lock, flags);
>         if (!queuing_blocked(worker, work)) {
>                 kthread_insert_work(worker, work, &worker->work_list);
> @@ -895,6 +1011,7 @@ void kthread_delayed_work_timer_fn(struct timer_list *t)
>  
>         /* Move the work from worker->delayed_work_list. */
>         WARN_ON_ONCE(list_empty(&work->node));
> +       debug_kwork_deactivate(work);
>         list_del_init(&work->node);
>         kthread_insert_work(worker, work, &worker->work_list);
>  
> @@ -924,7 +1041,7 @@ static void __kthread_queue_delayed_work(struct kthread_worker *worker,
>  
>         /* Be paranoid and try to detect possible races already now. */
>         kthread_insert_work_sanity_check(worker, work);
> -
> +       debug_kwork_activate(work);
>         list_add(&work->node, &worker->delayed_work_list);
>         work->worker = worker;
>         timer->expires = jiffies + delay;
> @@ -954,6 +1071,7 @@ bool kthread_queue_delayed_work(struct kthread_worker *worker,
>         unsigned long flags;
>         bool ret = false;
>  
> +       debug_kwork_assert_init(work);
>         raw_spin_lock_irqsave(&worker->lock, flags);
>  
>         if (!queuing_blocked(worker, work)) {
> @@ -987,15 +1105,16 @@ static void kthread_flush_work_fn(struct kthread_work *work)
>  void kthread_flush_work(struct kthread_work *work)
>  {
>         struct kthread_flush_work fwork = {
> -               KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
> -               COMPLETION_INITIALIZER_ONSTACK(fwork.done),
> +               .done = COMPLETION_INITIALIZER_ONSTACK(fwork.done),
>         };
>         struct kthread_worker *worker;
>         bool noop = false;
>  
> +       kthread_init_work_onstack(&fwork.work, kthread_flush_work_fn);
> +       debug_kwork_assert_init(work);
>         worker = work->worker;
>         if (!worker)
> -               return;
> +               goto out;

Why make the worker and init it on the stack if there isn't anything to
do? The !worker check should be early and then bail out before doing
anything else.

>  
>         raw_spin_lock_irq(&worker->lock);
>         /* Work must not be used with >1 worker, see kthread_queue_work(). */
> @@ -1013,6 +1132,9 @@ void kthread_flush_work(struct kthread_work *work)
>  
>         if (!noop)
>                 wait_for_completion(&fwork.done);
> +
> +out:

Then this label can be dropped.

> +       destroy_kwork_on_stack(&fwork.work);
>  }
>  EXPORT_SYMBOL_GPL(kthread_flush_work);
>