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

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Message-ID: <20250918114610.GZ3419281@noisy.programming.kicks-ass.net>
Date: Thu, 18 Sep 2025 13:46:10 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...nel.org>
Cc: 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



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(-)

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;