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

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Message-ID: <20250918111853.5dc424df@gandalf.local.home>
Date: Thu, 18 Sep 2025 11:18:53 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
 Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Arnaldo
 Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Andrii Nakryiko <andrii@...nel.org>,
 Indu Bhagat <indu.bhagat@...cle.com>, "Jose E. Marchesi" <jemarch@....org>,
 Beau Belgrave <beaub@...ux.microsoft.com>, Jens Remus
 <jremus@...ux.ibm.com>, Linus Torvalds <torvalds@...ux-foundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>, Florian Weimer
 <fweimer@...hat.com>, Sam James <sam@...too.org>, Kees Cook
 <kees@...nel.org>, Carlos O'Donell <codonell@...hat.com>
Subject: Re: [RESEND][PATCH v15 0/4] perf: Support the deferred unwinding
 infrastructure

On Thu, 18 Sep 2025 13:46:10 +0200
Peter Zijlstra <peterz@...radead.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;