From 5c0985dd3c32fc2bbd0e8beaf13cf52cd97376a2 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Mon, 24 Aug 2026 14:08:20 +0200 Subject: [PATCH] pid_namespace: prevent TIF_NOTIFY_SIGNAL from interrupting the reaper Since commit 7fea700e04bd ("zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING") zap_pid_ns_processes() clears TIF_NOTIFY_SIGNAL before every kernel_wait4() call. Otherwise kernel_wait4() doesn't sleep and returns -ERESTARTSYS if signal_pending() is true and the reaper busy-waits. But clearing TIF_NOTIFY_SIGNAL doesn't fix it. It can get raised again. For example, klp_send_signals() sets it raw against any task that hasn't transitioned yet. And it keeps sending it until the livepatch finishes. The sleep loop waiting for pid_allocated to drop has the same problem and it doesn't even clear anything. So a schedule() in TASK_INTERRUPTIBLE returns immediately. Use a no_notify_signal guard. signal_pending() will ignore TIF_NOTIFY_SIGNAL and the pid namespace reaper sleeps until a child exits or free_pid() wakes it. Link: https://patch.msgid.link/20260824-work-tif_notify_signal-v2-5-6609e42b3157@kernel.org Fixes: 7fea700e04bd ("zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING") Reviewed-by: Oleg Nesterov Cc: stable@vger.kernel.org Suggested-by: Oleg Nesterov Signed-off-by: Christian Brauner (Amutable) --- kernel/pid_namespace.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index d36afc58ee1d..8bc9edb40b78 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -238,9 +238,10 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns) * kernel_wait4() will also block until our children traced from the * parent namespace are detached and become EXIT_DEAD. */ + /* Task work must not busy-loop the reaper, see signal_pending(). */ + guard(no_notify_signal)(); do { clear_thread_flag(TIF_SIGPENDING); - clear_thread_flag(TIF_NOTIFY_SIGNAL); rc = kernel_wait4(-1, NULL, __WALL, NULL); } while (rc != -ECHILD);