livepatch: Replace the fake signal sending with TIF_NOTIFY_SIGNAL infrastructure

Livepatch sends a fake signal to all remaining blocking tasks of a
running transition after a set period of time. It uses TIF_SIGPENDING
flag for the purpose. Commit 12db8b6900 ("entry: Add support for
TIF_NOTIFY_SIGNAL") added a generic infrastructure to achieve the same.
Replace our bespoke solution with the generic one.

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

kernel/livepatch/transition.c

@@ -9,6 +9,7 @@
 
 #include <linux/cpu.h>
 #include <linux/stacktrace.h>
+#include <linux/tracehook.h>
 #include "core.h"
 #include "patch.h"
 #include "transition.h"
@@ -369,9 +370,7 @@ static void klp_send_signals(void)
 			 * Send fake signal to all non-kthread tasks which are
 			 * still not migrated.
 			 */
-			spin_lock_irq(&task->sighand->siglock);
+			set_notify_signal(task);
-			signal_wake_up(task, 0);
-			spin_unlock_irq(&task->sighand->siglock);
 		}
 	}
 	read_unlock(&tasklist_lock);

kernel/signal.c

@@ -43,7 +43,6 @@
 #include <linux/cn_proc.h>
 #include <linux/compiler.h>
 #include <linux/posix-timers.h>
-#include <linux/livepatch.h>
 #include <linux/cgroup.h>
 #include <linux/audit.h>
 
@@ -181,8 +180,7 @@ void recalc_sigpending_and_wake(struct task_struct *t)
 
 void recalc_sigpending(void)
 {
-	if (!recalc_sigpending_tsk(current) && !freezing(current) &&
+	if (!recalc_sigpending_tsk(current) && !freezing(current))
-	    !klp_patch_pending(current))
 		clear_thread_flag(TIF_SIGPENDING);
 
 }