rcu: Replace flush_signals() with WARN_ON(signal_pending())

Currently, when RCU awakens from a wait_event_interruptible() that
might have awakened prematurely, it does a flush_signals(). This is
done on the off-chance that someone figured out how to deliver a signal
to a kthread, which is supposed to be impossible.  Given that this
is supposed to be impossible, this commit changes the flush_signals()
calls into WARN_ON(signal_pending()).

Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

2 files changed, 5 insertions, 5 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9e83cd9a32f1..3e002c1cb441 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1796,7 +1796,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
                         if (rcu_gp_init(rsp))
                                 break;
                         cond_resched();
-                        flush_signals(current);
+                        WARN_ON(signal_pending(current));
                         trace_rcu_grace_period(rsp->name,
                                                ACCESS_ONCE(rsp->gpnum),
                                                TPS("reqwaitsig"));
@@ -1842,7 +1842,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
                         } else {
                                 /* Deal with stray signal. */
                                 cond_resched();
-                                flush_signals(current);
+                                WARN_ON(signal_pending(current));
                                 trace_rcu_grace_period(rsp->name,
                                                        ACCESS_ONCE(rsp->gpnum),
                                                        TPS("fqswaitsig"));
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index d67cc5c375c5..bbb0a0cd091b 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2237,7 +2237,7 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
                         (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
                 if (likely(d))
                         break;
-                flush_signals(current);
+                WARN_ON(signal_pending(current));
                 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
         }
         trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
@@ -2296,7 +2296,7 @@ wait_again:
                 if (!rcu_nocb_poll)
                         trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
                                             "WokeEmpty");
-                flush_signals(current);
+                WARN_ON(signal_pending(current));
                 schedule_timeout_interruptible(1);
 
                 /* Rescan in case we were a victim of memory ordering. */
@@ -2375,7 +2375,7 @@ static void nocb_follower_wait(struct rcu_data *rdp)
                 if (!rcu_nocb_poll)
                         trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
                                             "WokeEmpty");
-                flush_signals(current);
+                WARN_ON(signal_pending(current));
                 schedule_timeout_interruptible(1);
         }
 }