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pid_namespace: prevent TIF_NOTIFY_SIGNAL from interrupting the reaper

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Since commit 7fea700e04 ("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: 7fea700e04 ("zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING")
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: stable@vger.kernel.org
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2026-08-24 14:08:20 +02:00
parent d0ae35565f
commit 5c0985dd3c
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 2 additions and 1 deletions
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3
kernel/pid_namespace.c
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@ -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);