linux-kernel - [tip: perf/core] unwind: Make unwind_task_info::unwind

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Message-ID: <176173057318.2601451.3711090924055288815.tip-bot2@tip-bot2>
Date: Wed, 29 Oct 2025 09:36:13 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: perf/core] unwind: Make unwind_task_info::unwind_mask consistent

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     639214f65b1db87c6992eadf93079ff0d8768c2d
Gitweb:        https://git.kernel.org/tip/639214f65b1db87c6992eadf93079ff0d8768c2d
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 22 Sep 2025 16:09:17 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 29 Oct 2025 10:29:57 +01:00

unwind: Make unwind_task_info::unwind_mask consistent

The unwind_task_info::unwind_mask was manipulated using a mixture of:

  regular store
  WRITE_ONCE()
  try_cmpxchg()
  set_bit()
  atomic_long_*()

Clean up and make it consistently atomic_long_t.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://patch.msgid.link/20250924080119.384384486@infradead.org
---
 include/linux/unwind_deferred.h       |  4 ++--
 include/linux/unwind_deferred_types.h |  3 ++-
 kernel/unwind/deferred.c              | 17 +++++++++--------
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/include/linux/unwind_deferred.h b/include/linux/unwind_deferred.h
index 196e12c..f4743c8 100644
--- a/include/linux/unwind_deferred.h
+++ b/include/linux/unwind_deferred.h
@@ -46,7 +46,7 @@ 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 = info->unwind_mask;
+	unsigned long bits = atomic_long_read(&info->unwind_mask);
 
 	/* Was there any unwinding? */
 	if (likely(!bits))
@@ -56,7 +56,7 @@ static __always_inline void unwind_reset_info(void)
 		/* Is a task_work going to run again before going back */
 		if (bits & UNWIND_PENDING)
 			return;
-	} while (!try_cmpxchg(&info->unwind_mask, &bits, 0UL));
+	} while (!atomic_long_try_cmpxchg(&info->unwind_mask, &bits, 0UL));
 	current->unwind_info.id.id = 0;
 
 	if (unlikely(info->cache)) {
diff --git a/include/linux/unwind_deferred_types.h b/include/linux/unwind_deferred_types.h
index 29452ff..0a4c8dd 100644
--- a/include/linux/unwind_deferred_types.h
+++ b/include/linux/unwind_deferred_types.h
@@ -3,6 +3,7 @@
 #define _LINUX_UNWIND_USER_DEFERRED_TYPES_H
 
 #include <linux/types.h>
+#include <linux/atomic.h>
 
 struct unwind_cache {
 	unsigned long		unwind_completed;
@@ -32,7 +33,7 @@ union unwind_task_id {
 };
 
 struct unwind_task_info {
-	unsigned long		unwind_mask;
+	atomic_long_t		unwind_mask;
 	struct unwind_cache	*cache;
 	struct callback_head	work;
 	union unwind_task_id	id;
diff --git a/kernel/unwind/deferred.c b/kernel/unwind/deferred.c
index 09617d8..a88fb48 100644
--- a/kernel/unwind/deferred.c
+++ b/kernel/unwind/deferred.c
@@ -53,7 +53,7 @@ DEFINE_STATIC_SRCU(unwind_srcu);
 
 static inline bool unwind_pending(struct unwind_task_info *info)
 {
-	return test_bit(UNWIND_PENDING_BIT, &info->unwind_mask);
+	return atomic_long_read(&info->unwind_mask) & UNWIND_PENDING;
 }
 
 /*
@@ -141,7 +141,7 @@ int unwind_user_faultable(struct unwind_stacktrace *trace)
 	cache->nr_entries = trace->nr;
 
 	/* Clear nr_entries on way back to user space */
-	set_bit(UNWIND_USED_BIT, &info->unwind_mask);
+	atomic_long_or(UNWIND_USED, &info->unwind_mask);
 
 	return 0;
 }
@@ -159,7 +159,7 @@ static void process_unwind_deferred(struct task_struct *task)
 
 	/* Clear pending bit but make sure to have the current bits */
 	bits = atomic_long_fetch_andnot(UNWIND_PENDING,
-				  (atomic_long_t *)&info->unwind_mask);
+					&info->unwind_mask);
 	/*
 	 * From here on out, the callback must always be called, even if it's
 	 * just an empty trace.
@@ -264,7 +264,7 @@ int unwind_deferred_request(struct unwind_work *work, u64 *cookie)
 
 	*cookie = get_cookie(info);
 
-	old = READ_ONCE(info->unwind_mask);
+	old = atomic_long_read(&info->unwind_mask);
 
 	/* Is this already queued or executed */
 	if (old & bit)
@@ -277,7 +277,7 @@ int unwind_deferred_request(struct unwind_work *work, u64 *cookie)
 	 * to have a callback.
 	 */
 	bits = UNWIND_PENDING | bit;
-	old = atomic_long_fetch_or(bits, (atomic_long_t *)&info->unwind_mask);
+	old = atomic_long_fetch_or(bits, &info->unwind_mask);
 	if (old & bits) {
 		/*
 		 * If the work's bit was set, whatever set it had better
@@ -291,7 +291,7 @@ int unwind_deferred_request(struct unwind_work *work, u64 *cookie)
 	ret = task_work_add(current, &info->work, twa_mode);
 
 	if (WARN_ON_ONCE(ret))
-		WRITE_ONCE(info->unwind_mask, 0);
+		atomic_long_set(&info->unwind_mask, 0);
 
 	return ret;
 }
@@ -323,7 +323,8 @@ void unwind_deferred_cancel(struct unwind_work *work)
 	guard(rcu)();
 	/* Clear this bit from all threads */
 	for_each_process_thread(g, t) {
-		clear_bit(bit, &t->unwind_info.unwind_mask);
+		atomic_long_andnot(BIT(bit),
+				   &t->unwind_info.unwind_mask);
 		if (t->unwind_info.cache)
 			clear_bit(bit, &t->unwind_info.cache->unwind_completed);
 	}
@@ -353,7 +354,7 @@ void unwind_task_init(struct task_struct *task)
 
 	memset(info, 0, sizeof(*info));
 	init_task_work(&info->work, unwind_deferred_task_work);
-	info->unwind_mask = 0;
+	atomic_long_set(&info->unwind_mask, 0);
 }
 
 void unwind_task_free(struct task_struct *task)