[PATCH 2/2] dequeue_synchronous_signal: kill the unnecessary still-pending check

[Oleg Nesterov <oleg@redhat.com>]

The signals in SYNCHRONOUS_MASK are not real-time signals, so at most
one instance can be queued. Add a static_assert() to ensure.

Remove the list_for_each_entry_continue() loop and simplify the code.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/signal.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 9924489c43a5..529774926476 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -665,6 +665,8 @@ int dequeue_signal(sigset_t *mask, kernel_siginfo_t *info, enum pid_type *type)
 }
 EXPORT_SYMBOL_GPL(dequeue_signal);
 
+static_assert(ilog2(SYNCHRONOUS_MASK) + 1 < SIGRTMIN);
+
 static int dequeue_synchronous_signal(kernel_siginfo_t *info)
 {
 	struct task_struct *tsk = current;
@@ -676,7 +678,6 @@ static int dequeue_synchronous_signal(kernel_siginfo_t *info)
 	 */
 	if (!((pending->signal.sig[0] & ~tsk->blocked.sig[0]) & SYNCHRONOUS_MASK))
 		return 0;
-
 	/*
 	 * Return the first synchronous signal in the queue.
 	 */
@@ -685,22 +686,14 @@ static int dequeue_synchronous_signal(kernel_siginfo_t *info)
 		if (SI_FROMKERNEL(&q->info) &&
 		    (sigmask(q->info.si_signo) & SYNCHRONOUS_MASK)) {
 			sync = q;
-			goto next;
+			break;
 		}
 	}
-	return 0;
-next:
-	/*
-	 * Check if there is another siginfo for the same signal.
-	 */
-	list_for_each_entry_continue(q, &pending->list, list) {
-		if (q->info.si_signo == sync->info.si_signo)
-			goto still_pending;
-	}
+	if (!sync)
+		return 0;
 
 	sigdelset(&pending->signal, sync->info.si_signo);
 	recalc_sigpending();
-still_pending:
 	list_del_init(&sync->list);
 	copy_siginfo(info, &sync->info);
 	__sigqueue_free(sync);
-- 
2.52.0