[PATCH v18 03/11] perf/hw_breakpoint: Add register_wide_hw_breakpoint_cpuslocked() API

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add register_wide_hw_breakpoint_cpuslocked() which registers a wide
hardware breakpoint across all online CPUs while caller holds
cpus_read_lock(). This allows callers who need to perform additional
setup under cpus_read_lock() without releasing it to avoid races with
CPU hotplug and without triggering recursive lockdep warnings.

Refactor register_wide_hw_breakpoint() as a wrapper around
register_wide_hw_breakpoint_cpuslocked().

Assisted-by: LLM
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 include/linux/hw_breakpoint.h |    9 +++++++++
 kernel/events/hw_breakpoint.c |   38 ++++++++++++++++++++++++++++++++------
 2 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index bf65c7fffd99..65efe55fef14 100644
--- a/include/linux/hw_breakpoint.h
+++ b/include/linux/hw_breakpoint.h
@@ -76,6 +76,11 @@ register_wide_hw_breakpoint_cpu(struct perf_event_attr *attr,
 				void *context,
 				int cpu);
 
+extern struct perf_event * __percpu *
+register_wide_hw_breakpoint_cpuslocked(struct perf_event_attr *attr,
+				       perf_overflow_handler_t triggered,
+				       void *context);
+
 extern struct perf_event * __percpu *
 register_wide_hw_breakpoint(struct perf_event_attr *attr,
 			    perf_overflow_handler_t triggered,
@@ -123,6 +128,10 @@ register_wide_hw_breakpoint_cpu(struct perf_event_attr *attr,
 				void *context,
 				int cpu)		{ return NULL; }
 static inline struct perf_event * __percpu *
+register_wide_hw_breakpoint_cpuslocked(struct perf_event_attr *attr,
+				       perf_overflow_handler_t triggered,
+				       void *context)		{ return NULL; }
+static inline struct perf_event * __percpu *
 register_wide_hw_breakpoint(struct perf_event_attr *attr,
 			    perf_overflow_handler_t triggered,
 			    void *context)		{ return NULL; }
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 69bfb17b87c4..5627ad97600a 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -832,27 +832,30 @@ void unregister_hw_breakpoint(struct perf_event *bp)
 EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 
 /**
- * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
+ * register_wide_hw_breakpoint_cpuslocked - register a wide breakpoint with cpus locked
  * @attr: breakpoint attributes
  * @triggered: callback to trigger when we hit the breakpoint
  * @context: context data could be used in the triggered callback
  *
+ * Same as register_wide_hw_breakpoint(), but caller must hold cpus_read_lock().
+ *
  * @return a set of per_cpu pointers to perf events
  */
 struct perf_event * __percpu *
-register_wide_hw_breakpoint(struct perf_event_attr *attr,
-			    perf_overflow_handler_t triggered,
-			    void *context)
+register_wide_hw_breakpoint_cpuslocked(struct perf_event_attr *attr,
+				       perf_overflow_handler_t triggered,
+				       void *context)
 {
 	struct perf_event * __percpu *cpu_events, *bp;
 	long err = 0;
 	int cpu;
 
+	lockdep_assert_cpus_held();
+
 	cpu_events = alloc_percpu(typeof(*cpu_events));
 	if (!cpu_events)
 		return ERR_PTR_PCPU(-ENOMEM);
 
-	cpus_read_lock();
 	for_each_online_cpu(cpu) {
 		bp = perf_event_create_kernel_counter(attr, cpu, NULL,
 						      triggered, context);
@@ -863,7 +866,6 @@ register_wide_hw_breakpoint(struct perf_event_attr *attr,
 
 		per_cpu(*cpu_events, cpu) = bp;
 	}
-	cpus_read_unlock();
 
 	if (likely(!err))
 		return cpu_events;
@@ -871,6 +873,30 @@ register_wide_hw_breakpoint(struct perf_event_attr *attr,
 	unregister_wide_hw_breakpoint(cpu_events);
 	return ERR_PTR_PCPU(err);
 }
+EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint_cpuslocked);
+
+/**
+ * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
+ * @attr: breakpoint attributes
+ * @triggered: callback to trigger when we hit the breakpoint
+ * @context: context data could be used in the triggered callback
+ *
+ * @return a set of per_cpu pointers to perf events
+ */
+struct perf_event * __percpu *
+register_wide_hw_breakpoint(struct perf_event_attr *attr,
+			    perf_overflow_handler_t triggered,
+			    void *context)
+{
+	struct perf_event * __percpu *cpu_events;
+
+	cpus_read_lock();
+	cpu_events = register_wide_hw_breakpoint_cpuslocked(attr, triggered,
+							    context);
+	cpus_read_unlock();
+
+	return cpu_events;
+}
 EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 
 /**