Re: [RESEND][PATCH v15 0/4] perf: Support the deferred unwinding infrastructure

[Steven Rostedt]

On Thu, 18 Sep 2025 13:46:10 +0200
Peter Zijlstra <pet...@infradead.org> wrote:

> So I started looking at this, but given I never seen the deferred unwind
> bits that got merged I have to look at that first.
> 
> Headers want something like so.. Let me read the rest.
> 
> ---
>  include/linux/unwind_deferred.h       | 38 
> +++++++++++++++++++----------------
>  include/linux/unwind_deferred_types.h |  2 ++
>  2 files changed, 23 insertions(+), 17 deletions(-)

Would you like to send a formal patch with this? I'd actually break it into
two patches. One to clean up the long lines, and the other to change the
logic.

-- Steve


> 
> diff --git a/include/linux/unwind_deferred.h b/include/linux/unwind_deferred.h
> index 26122d00708a..5d51a3f2f8ec 100644
> --- a/include/linux/unwind_deferred.h
> +++ b/include/linux/unwind_deferred.h
> @@ -8,7 +8,8 @@
>  
>  struct unwind_work;
>  
> -typedef void (*unwind_callback_t)(struct unwind_work *work, struct 
> unwind_stacktrace *trace, u64 cookie);
> +typedef void (*unwind_callback_t)(struct unwind_work *work,
> +                               struct unwind_stacktrace *trace, u64 cookie);
>  
>  struct unwind_work {
>       struct list_head                list;
> @@ -44,22 +45,22 @@ void unwind_deferred_task_exit(struct task_struct *task);
>  static __always_inline void unwind_reset_info(void)
>  {
>       struct unwind_task_info *info = &current->unwind_info;
> -     unsigned long bits;
> +     unsigned long bits = info->unwind_mask;
>  
>       /* Was there any unwinding? */
> -     if (unlikely(info->unwind_mask)) {
> -             bits = info->unwind_mask;
> -             do {
> -                     /* Is a task_work going to run again before going back 
> */
> -                     if (bits & UNWIND_PENDING)
> -                             return;
> -             } while (!try_cmpxchg(&info->unwind_mask, &bits, 0UL));
> -             current->unwind_info.id.id = 0;
> +     if (likely(!bits))
> +             return;
>  
> -             if (unlikely(info->cache)) {
> -                     info->cache->nr_entries = 0;
> -                     info->cache->unwind_completed = 0;
> -             }
> +     do {
> +             /* Is a task_work going to run again before going back */
> +             if (bits & UNWIND_PENDING)
> +                     return;
> +     } while (!try_cmpxchg(&info->unwind_mask, &bits, 0UL));
> +     current->unwind_info.id.id = 0;
> +
> +     if (unlikely(info->cache)) {
> +             info->cache->nr_entries = 0;
> +             info->cache->unwind_completed = 0;
>       }
>  }
>  
> @@ -68,9 +69,12 @@ static __always_inline void unwind_reset_info(void)
>  static inline void unwind_task_init(struct task_struct *task) {}
>  static inline void unwind_task_free(struct task_struct *task) {}
>  
> -static inline int unwind_user_faultable(struct unwind_stacktrace *trace) { 
> return -ENOSYS; }
> -static inline int unwind_deferred_init(struct unwind_work *work, 
> unwind_callback_t func) { return -ENOSYS; }
> -static inline int unwind_deferred_request(struct unwind_work *work, u64 
> *timestamp) { return -ENOSYS; }
> +static inline int unwind_user_faultable(struct unwind_stacktrace *trace)
> +{ return -ENOSYS; }
> +static inline int unwind_deferred_init(struct unwind_work *work, 
> unwind_callback_t func)
> +{ return -ENOSYS; }
> +static inline int unwind_deferred_request(struct unwind_work *work, u64 
> *timestamp)
> +{ return -ENOSYS; }
>  static inline void unwind_deferred_cancel(struct unwind_work *work) {}
>  
>  static inline void unwind_deferred_task_exit(struct task_struct *task) {}
> diff --git a/include/linux/unwind_deferred_types.h 
> b/include/linux/unwind_deferred_types.h
> index 33b62ac25c86..29452ff49859 100644
> --- a/include/linux/unwind_deferred_types.h
> +++ b/include/linux/unwind_deferred_types.h
> @@ -2,6 +2,8 @@
>  #ifndef _LINUX_UNWIND_USER_DEFERRED_TYPES_H
>  #define _LINUX_UNWIND_USER_DEFERRED_TYPES_H
>  
> +#include <linux/types.h>
> +
>  struct unwind_cache {
>       unsigned long           unwind_completed;
>       unsigned int            nr_entries;