recalc_sigpending_tsk fixes

Steve Hawkes discovered a problem where recalc_sigpending_tsk was called in do_sigaction but no signal_wake_up call was made, preventing later signals from waking up blocked threads with TIF_SIGPENDING already set. In fact, the few other calls to recalc_sigpending_tsk outside the signals code are also subject to this problem in other race conditions. This change makes recalc_sigpending_tsk private to the signals code. It changes the outside calls, as well as do_sigaction, to use the new recalc_sigpending_and_wake instead.

Roland McGrath committed 19 years ago

Commit 7bb44ad1 parent 3c6df2a4 files · +28 −17Browse files

Showing the changes to kernel (3 of 4 files). Show all

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3 files

kernel/exit.c +2 −5
kernel/power/process.c +1 −1
kernel/signal.c +18 −6

kernel/exit.c+2−5

 		read_lock(&tasklist_lock);
 		spin_lock_irq(&tsk->sighand->siglock);
 		for (t = next_thread(tsk); t != tsk; t = next_thread(t))
-			if (!signal_pending(t) && !(t->flags & PF_EXITING)) {
+			if (!signal_pending(t) && !(t->flags & PF_EXITING))
-				recalc_sigpending_tsk(t);
+				recalc_sigpending_and_wake(t);
-				if (signal_pending(t))
-					signal_wake_up(t, 0);
-			}
 		spin_unlock_irq(&tsk->sighand->siglock);
 		read_unlock(&tasklist_lock);
 	}

kernel/power/process.c+1−1

@@ -101,7 +101,7 @@ static void cancel_freezing(struct task_struct *p) · 100 unmodified lines
101	pr_debug(" clean up: %s\n", p->comm);	101	pr_debug(" clean up: %s\n", p->comm);
102	do_not_freeze(p);	102	do_not_freeze(p);
103	spin_lock_irqsave(&p->sighand->siglock, flags);	103	spin_lock_irqsave(&p->sighand->siglock, flags);
104	recalc_sigpending_tsk(p);	104	recalc_sigpending_and_wake(p);
105	spin_unlock_irqrestore(&p->sighand->siglock, flags);	105	spin_unlock_irqrestore(&p->sighand->siglock, flags);
106	}	106	}
107	}	107	}

kernel/signal.c+18−6

 #define PENDING(p,b) has_pending_signals(&(p)->signal, (b))
-fastcall void recalc_sigpending_tsk(struct task_struct *t)
+static int recalc_sigpending_tsk(struct task_struct *t)
 {
 	if (t->signal->group_stop_count > 0 ||
 	    (freezing(t)) ||
 	    PENDING(&t->pending, &t->blocked) ||
-	    PENDING(&t->signal->shared_pending, &t->blocked))
+	    PENDING(&t->signal->shared_pending, &t->blocked)) {
 		set_tsk_thread_flag(t, TIF_SIGPENDING);
-	else
+		return 1;
-		clear_tsk_thread_flag(t, TIF_SIGPENDING);
+	}
+	clear_tsk_thread_flag(t, TIF_SIGPENDING);
+	return 0;
+}
+/*
+ * After recalculating TIF_SIGPENDING, we need to make sure the task wakes up.
+ * This is superfluous when called on current, the wakeup is a harmless no-op.
+ */
+void recalc_sigpending_and_wake(struct task_struct *t)
+{
+	if (recalc_sigpending_tsk(t))
+		signal_wake_up(t, 0);
 }
 void recalc_sigpending(void)
 		action->sa.sa_handler = SIG_DFL;
 		if (blocked) {
 			sigdelset(&t->blocked, sig);
-			recalc_sigpending_tsk(t);
+			recalc_sigpending_and_wake(t);
 		}
 	}
 	ret = specific_send_sig_info(sig, info, t);
 			rm_from_queue_full(&mask, &t->signal->shared_pending);
 			do {
 				rm_from_queue_full(&mask, &t->pending);
-				recalc_sigpending_tsk(t);
+				recalc_sigpending_and_wake(t);
 				t = next_thread(t);
 			} while (t != current);
 		}