Reuse start_task_exit_locked to implement start_task_exit.

Simplify the exit logic by having all exits go through get_signal.
This simplifies the analysis of syncrhonization during exit and
gurantees a full set of registers will be available for ptrace to
examine at PTRACE_EVENT_EXIT.

Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/sched/signal.h |  1 +
 kernel/exit.c                |  4 +++-
 kernel/seccomp.c             |  2 +-
 kernel/signal.c              | 12 ++++++++++++
 4 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index a958381ba4a9..3f4e69c019b7 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h

@@ -430,6 +430,7 @@ static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
 
 void start_group_exit(int exit_code);
 void start_task_exit_locked(struct task_struct *task, int exit_code);
+void start_task_exit(int exit_code);
 
 void task_join_group_stop(struct task_struct *task);
 

diff --git a/kernel/exit.c b/kernel/exit.c
index 635f434122b7..51e0c82b3f7d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c

@@ -889,7 +889,9 @@ EXPORT_SYMBOL(complete_and_exit);
 
 SYSCALL_DEFINE1(exit, int, error_code)
 {
-	do_exit((error_code&0xff)<<8);
+	start_task_exit((error_code&0xff)<<8);
+	/* get_signal will call do_exit */
+	return 0;
 }
 
 

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index b1c06fd1b205..e0c4c123a8bf 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c

@@ -1248,7 +1248,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 			force_sig_seccomp(this_syscall, data, true);
 		} else {
 			if (action == SECCOMP_RET_KILL_THREAD)
-				do_exit(SIGSYS);
+				start_task_exit(SIGSYS);
 			else
 				start_group_exit(SIGSYS);
 		}

diff --git a/kernel/signal.c b/kernel/signal.c
index afbc001220dd..63fda9b6bbf9 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c

@@ -1424,6 +1424,18 @@ void start_task_exit_locked(struct task_struct *task, int exit_code)
 	}
 }
 
+void start_task_exit(int exit_code)
+{
+	struct task_struct *task = current;
+	if (!fatal_signal_pending(task)) {
+		struct sighand_struct *const sighand = task->sighand;
+		spin_lock_irq(&sighand->siglock);
+		if (!fatal_signal_pending(current))