[PATCH v2 2/2] kernel: rerun task_work while freezing in get_signal()

[Pavel Begunkov <asml.silence@xxxxxxxxx>]

io_uring can asynchronously add a task_work while the task is getting
freezed. TIF_NOTIFY_SIGNAL will prevent the task from sleeping in
do_freezer_trap(), and since the get_signal()'s relock loop doesn't
retry task_work, the task will spin there not being able to sleep
until the freezing is cancelled / the task is killed / etc.

Cc: stable@xxxxxxxxxxxxxxx
Link: https://github.com/systemd/systemd/issues/33626
Fixes: 12db8b690010c ("entry: Add support for TIF_NOTIFY_SIGNAL")
Reported-by: Julian Orth <ju.orth@xxxxxxxxx>
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 kernel/signal.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/signal.c b/kernel/signal.c
index 1f9dd41c04be..60c737e423a1 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2600,6 +2600,14 @@ static void do_freezer_trap(void)
 	spin_unlock_irq(&current->sighand->siglock);
 	cgroup_enter_frozen();
 	schedule();
+
+	/*
+	 * We could've been woken by task_work, run it to clear
+	 * TIF_NOTIFY_SIGNAL. The caller will retry if necessary.
+	 */
+	clear_notify_signal();
+	if (unlikely(task_work_pending(current)))
+		task_work_run();
 }
 
 static int ptrace_signal(int signr, kernel_siginfo_t *info, enum pid_type type)
-- 
2.44.0