[PATCH v1 1/2] perf record: Fix teardown hang on system-wide multi-threaded sessions

[Ian Rogers]

Under system-wide (-a) parallel streaming mode (--threads=cpu),
background recording threads can be inundated by a continuous
firehose of hardware samples generated by the OS. In this state,
a background thread's local hit count remains unequal to its
sample count, causing it to bypass the blocking fdarray__poll()
call entirely on each iteration of its recording loop.

Because the termination check relies on the POLLHUP event status
populated specifically by fdarray__poll(), bypassing it prevents
the background thread from ever recognizing that its control pipe
was closed by the main thread. This traps the background thread
in an infinite recording loop, hanging the main thread indefinitely
as it awaits a termination acknowledgment that never arrives.

Ensure teardown completion by adding explicit evlist__disable()
calls in the main thread's cleanup paths at out_child: and
out_child_no_flush:. Additionally, patch fdarray__filter() to
respect the fdarray_flag__nonfilterable flag, preventing it
from incorrectly setting the background thread's control pipe
file descriptor to -1 and clearing its revents mask upon
processing termination POLLHUP signals.

Fixes: f94563fac269 ("perf record: fix poll storm when monitored threads exit")
Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/lib/api/fd/array.c    | 6 ++++--
 tools/perf/builtin-record.c | 2 ++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/lib/api/fd/array.c b/tools/lib/api/fd/array.c
index ffe8272af59b..16a047f1906e 100644
--- a/tools/lib/api/fd/array.c
+++ b/tools/lib/api/fd/array.c
@@ -115,6 +115,9 @@ int fdarray__filter(struct fdarray *fda, short revents,
 		return 0;
 
 	for (fd = 0; fd < fda->nr; ++fd) {
+		if (fda->priv[fd].flags & fdarray_flag__nonfilterable)
+			continue;
+
 		if (!fda->entries[fd].events)
 			continue;
 
@@ -132,8 +135,7 @@ int fdarray__filter(struct fdarray *fda, short revents,
 			continue;
 		}
 
-		if (!(fda->priv[fd].flags & fdarray_flag__nonfilterable))
-			++nr;
+		++nr;
 	}
 
 	return nr;
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index ebd3ed0c9b3e..d1276382b77a 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -2890,11 +2890,13 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
 		record__synthesize_workload(rec, true);
 
 out_child:
+	evlist__disable(rec->evlist);
 	record__stop_threads(rec);
 	record__mmap_read_all(rec, true);
 	goto out_free_threads;
 out_child_no_flush:
 	/* mmap read already failed — retrying would just fail again */
+	evlist__disable(rec->evlist);
 	record__stop_threads(rec);
 out_free_threads:
 	record__free_thread_data(rec);
-- 
2.55.0.795.g602f6c329a-goog