[PATCH 6.19 839/844] tracing: Wake up poll waiters for hist files when removing an event

[Sasha Levin]

From: Petr Pavlu <petr.pavlu@xxxxxxxx>

[ Upstream commit 9678e53179aa7e907360f5b5b275769008a69b80 ]

The event_hist_poll() function attempts to verify whether an event file is
being removed, but this check may not occur or could be unnecessarily
delayed. This happens because hist_poll_wakeup() is currently invoked only
from event_hist_trigger() when a hist command is triggered. If the event
file is being removed, no associated hist command will be triggered and a
waiter will be woken up only after an unrelated hist command is triggered.

Fix the issue by adding a call to hist_poll_wakeup() in
remove_event_file_dir() after setting the EVENT_FILE_FL_FREED flag. This
ensures that a task polling on a hist file is woken up and receives
EPOLLERR.

Cc: stable@xxxxxxxxxxxxxxx
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Tom Zanussi <zanussi@xxxxxxxxxx>
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Link: https://patch.msgid.link/20260219162737.314231-3-petr.pavlu@xxxxxxxx
Fixes: 1bd13edbbed6 ("tracing/hist: Add poll(POLLIN) support on hist file")
Signed-off-by: Petr Pavlu <petr.pavlu@xxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/linux/trace_events.h | 5 +++++
 kernel/trace/trace_events.c  | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 3690221ba3d80..f925034e402dc 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -683,6 +683,11 @@ static inline void hist_poll_wakeup(void)
 
 #define hist_poll_wait(file, wait)	\
 	poll_wait(file, &hist_poll_wq, wait)
+
+#else
+static inline void hist_poll_wakeup(void)
+{
+}
 #endif
 
 #define __TRACE_EVENT_FLAGS(name, value)				\
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 2c6d3e33b9fb4..ec66170637102 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1295,6 +1295,9 @@ static void remove_event_file_dir(struct trace_event_file *file)
 	free_event_filter(file->filter);
 	file->flags |= EVENT_FILE_FL_FREED;
 	event_file_put(file);
+
+	/* Wake up hist poll waiters to notice the EVENT_FILE_FL_FREED flag. */
+	hist_poll_wakeup();
 }
 
 /*
-- 
2.51.0