linux-kernel - [PATCH] zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF

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Date: Sat, 8 Jun 2024 14:06:16 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Rachel Menge <rachelmenge@...ux.microsoft.com>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
	Wei Fu <fuweid89@...il.com>, apais@...ux.microsoft.com,
	Sudhanva Huruli <Sudhanva.Huruli@...rosoft.com>,
	Jens Axboe <axboe@...nel.dk>,
	Christian Brauner <brauner@...nel.org>,
	Mike Christie <michael.christie@...cle.com>,
	Joel Granados <j.granados@...sung.com>,
	Mateusz Guzik <mjguzik@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Subject: [PATCH] zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with
 TIF_SIGPENDING

kernel_wait4() doesn't sleep and returns -EINTR if there is no
eligible child and signal_pending() is true.

That is why zap_pid_ns_processes() clears TIF_SIGPENDING but this is not
enough, it should also clear TIF_NOTIFY_SIGNAL to make signal_pending()
return false and avoid a busy-wait loop.

Fixes: 12db8b690010 ("entry: Add support for TIF_NOTIFY_SIGNAL")
Reported-by: Rachel Menge <rachelmenge@...ux.microsoft.com>
Closes: https://lore.kernel.org/all/1386cd49-36d0-4a5c-85e9-bc42056a5a38@linux.microsoft.com/
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/pid_namespace.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index dc48fecfa1dc..25f3cf679b35 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -218,6 +218,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 	 */
 	do {
 		clear_thread_flag(TIF_SIGPENDING);
+		clear_thread_flag(TIF_NOTIFY_SIGNAL);
 		rc = kernel_wait4(-1, NULL, __WALL, NULL);
 	} while (rc != -ECHILD);
 
-- 
2.25.1.362.g51ebf55