[PATCH 4/4] task_work: simplify the usage in ptrace_notify() and get_signal_to_deliver()

[Oleg Nesterov <oleg@redhat.com>]

ptrace_notify() and get_signal_to_deliver() do unnecessary things
before task_work_run().

1. smp_mb__after_clear_bit() is not needed, test_and_clear_bit()
   implies mb().

2. And we do not need the barrier at all, in this case we only
   care about the "synchronous" works added by the task itself.

3. No need to clear TIF_NOTIFY_RESUME, and we should not assume
   task_works is the only user of this flag.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/signal.c |   18 ++++--------------
 1 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index be4f856..2c681f1 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1971,13 +1971,8 @@ static void ptrace_do_notify(int signr, int exit_code, int why)
 void ptrace_notify(int exit_code)
 {
 	BUG_ON((exit_code & (0x7f | ~0xffff)) != SIGTRAP);
-	if (unlikely(current->task_works)) {
-		if (test_and_clear_ti_thread_flag(current_thread_info(),
-						   TIF_NOTIFY_RESUME)) {
-			smp_mb__after_clear_bit();
-			task_work_run();
-		}
-	}
+	if (unlikely(current->task_works))
+		task_work_run();
 
 	spin_lock_irq(&current->sighand->siglock);
 	ptrace_do_notify(SIGTRAP, exit_code, CLD_TRAPPED);
@@ -2198,13 +2193,8 @@ int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
 	struct signal_struct *signal = current->signal;
 	int signr;
 
-	if (unlikely(current->task_works)) {
-		if (test_and_clear_ti_thread_flag(current_thread_info(),
-						   TIF_NOTIFY_RESUME)) {
-			smp_mb__after_clear_bit();
-			task_work_run();
-		}
-	}
+	if (unlikely(current->task_works))
+		task_work_run();
 
 	if (unlikely(uprobe_deny_signal()))
 		return 0;
-- 
1.5.5.1