Commit 82d94856 authored Jan 09, 2018 by Peter Zijlstra Committed by Ingo Molnar Jan 25, 2018

perf/core: Fix lock inversion between perf,trace,cpuhp



Lockdep gifted us with noticing the following 4-way lockup scenario:

        perf_trace_init()
 #0       mutex_lock(&event_mutex)
          perf_trace_event_init()
            perf_trace_event_reg()
              tp_event->class->reg() := tracepoint_probe_register
 #1             mutex_lock(&tracepoints_mutex)
                  trace_point_add_func()
 #2                 static_key_enable()

 #2     do_cpu_up()
          perf_event_init_cpu()
 #3         mutex_lock(&pmus_lock)
 #4         mutex_lock(&ctx->mutex)

        perf_event_task_disable()
          mutex_lock(&current->perf_event_mutex)
 #4       ctx = perf_event_ctx_lock()
 #5       perf_event_for_each_child()

        do_exit()
          task_work_run()
            __fput()
              perf_release()
                perf_event_release_kernel()
 #4               mutex_lock(&ctx->mutex)
 #5               mutex_lock(&event->child_mutex)
                  free_event()
                    _free_event()
                      event->destroy() := perf_trace_destroy
 #0                     mutex_lock(&event_mutex);

Fix that by moving the free_event() out from under the locks.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 1f07476e

kernel/events/core.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -1231,6 +1231,10 @@ static void put_ctx(struct perf_event_context *ctx)
		* perf_event_context::lock
		* perf_event::mmap_mutex
		* mmap_sem
		*
		* cpu_hotplug_lock
		* pmus_lock
		* cpuctx->mutex / perf_event_context::mutex
		*/
		static struct perf_event_context *
		perf_event_ctx_lock_nested(struct perf_event *event, int nesting)
		@@ -4196,6 +4200,7 @@ int perf_event_release_kernel(struct perf_event *event)
		{
		struct perf_event_context *ctx = event->ctx;
		struct perf_event child, tmp;
		LIST_HEAD(free_list);

		/*
		* If we got here through err_file: fput(event_file); we will not have
		@@ -4268,8 +4273,7 @@ again:
		struct perf_event, child_list);
		if (tmp == child) {
		perf_remove_from_context(child, DETACH_GROUP);
		list_del(&child->child_list);
		free_event(child);
		list_move(&child->child_list, &free_list);
		/*
		* This matches the refcount bump in inherit_event();
		* this can't be the last reference.
		@@ -4284,6 +4288,11 @@ again:
		}
		mutex_unlock(&event->child_mutex);

		list_for_each_entry_safe(child, tmp, &free_list, child_list) {
		list_del(&child->child_list);
		free_event(child);
		}

		no_ctx:
		put_event(event); /* Must be the 'last' reference */
		return 0;

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