perf thread: Remove notion of dead threads

The dead thread list is best effort. Threads live on it until the
reference count hits zero and they are removed. With correct reference
counting this should never happen. It is, however, part of the 'perf
sched' output that is now removed. If this is an issue we should
implement tracking of dead threads in a robust not best-effort way.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ali Saidi <alisaidi@amazon.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Brian Robbins <brianrob@linux.microsoft.com>
Cc: Changbin Du <changbin.du@huawei.com>
Cc: Dmitrii Dolgov <9erthalion6@gmail.com>
Cc: Fangrui Song <maskray@google.com>
Cc: German Gomez <german.gomez@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ivan Babrou <ivan@cloudflare.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Steinar H. Gunderson <sesse@google.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Wenyu Liu <liuwenyu7@huawei.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Jihong <yangjihong1@huawei.com>
Cc: Ye Xingchen <ye.xingchen@zte.com.cn>
Cc: Yuan Can <yuancan@huawei.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20230608232823.4027869-2-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 1 insertions, 31 deletions

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 9e02e19c1b7a..a1954ac85f59 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -241,17 +241,6 @@ void machine__exit(struct machine *machine)
 
 	for (i = 0; i < THREADS__TABLE_SIZE; i++) {
 		struct threads *threads = &machine->threads[i];
-		struct thread *thread, *n;
-		/*
-		 * Forget about the dead, at this point whatever threads were
-		 * left in the dead lists better have a reference count taken
-		 * by who is using them, and then, when they drop those references
-		 * and it finally hits zero, thread__put() will check and see that
-		 * its not in the dead threads list and will not try to remove it
-		 * from there, just calling thread__delete() straight away.
-		 */
-		list_for_each_entry_safe(thread, n, &threads->dead, node)
-			list_del_init(&thread->node);
 
 		exit_rwsem(&threads->lock);
 	}
@@ -2046,18 +2035,7 @@ static void __machine__remove_thread(struct machine *machine, struct thread *th,
 	rb_erase_cached(&th->rb_node, &threads->entries);
 	RB_CLEAR_NODE(&th->rb_node);
 	--threads->nr;
-	/*
-	 * Move it first to the dead_threads list, then drop the reference,
-	 * if this is the last reference, then the thread__delete destructor
-	 * will be called and we will remove it from the dead_threads list.
-	 */
-	list_add_tail(&th->node, &threads->dead);
 
-	/*
-	 * We need to do the put here because if this is the last refcount,
-	 * then we will be touching the threads->dead head when removing the
-	 * thread.
-	 */
 	thread__put(th);
 
 	if (lock)
@@ -2145,10 +2123,8 @@ int machine__process_exit_event(struct machine *machine, union perf_event *event
 	if (dump_trace)
 		perf_event__fprintf_task(event, stdout);
 
-	if (thread != NULL) {
-		thread__exited(thread);
+	if (thread != NULL)
 		thread__put(thread);
-	}
 
 	return 0;
 }
@@ -3204,12 +3180,6 @@ int machine__for_each_thread(struct machine *machine,
 			if (rc != 0)
 				return rc;
 		}
-
-		list_for_each_entry(thread, &threads->dead, node) {
-			rc = fn(thread, priv);
-			if (rc != 0)
-				return rc;
-		}
 	}
 	return rc;
 }