[PATCH 2/2] posix timers: discard SI_TIMER signals on exec

[Oleg Nesterov]

Based on Roland's patch. This approach was suggested by Austin Clements
from the very beginning, and then by Linus.

As Austin pointed out, the execing task can be killed by SI_TIMER signal
because exec flushes the signal handlers, but doesn't discard the pending
signals generated by posix timers. Perhaps not a bug, but people find this
surprising. See http://bugzilla.kernel.org/show_bug.cgi?id=10460

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

 include/linux/sched.h |    2 ++
 fs/exec.c             |    1 +
 kernel/signal.c       |   34 ++++++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+)

--- 26-rc2/include/linux/sched.h~2_FLUSH_SI_TIMER_ON_EXEC	2008-05-18 20:08:13.000000000 +0400
+++ 26-rc2/include/linux/sched.h	2008-05-18 15:44:16.000000000 +0400
@@ -1849,7 +1849,9 @@ extern void exit_thread(void);
 extern void exit_files(struct task_struct *);
 extern void __cleanup_signal(struct signal_struct *);
 extern void __cleanup_sighand(struct sighand_struct *);
+
 extern void exit_itimers(struct signal_struct *);
+extern void flush_itimer_signals(void);
 
 extern NORET_TYPE void do_group_exit(int);
 
--- 26-rc2/fs/exec.c~2_FLUSH_SI_TIMER_ON_EXEC	2008-05-18 18:36:30.000000000 +0400
+++ 26-rc2/fs/exec.c	2008-05-26 19:37:35.000000000 +0400
@@ -860,6 +860,7 @@ static int de_thread(struct task_struct 
 
 no_thread_group:
 	exit_itimers(sig);
+	flush_itimer_signals();
 	if (leader)
 		release_task(leader);
 
--- 26-rc2/kernel/signal.c~2_FLUSH_SI_TIMER_ON_EXEC	2008-05-26 18:13:08.000000000 +0400
+++ 26-rc2/kernel/signal.c	2008-05-26 20:13:50.000000000 +0400
@@ -231,6 +231,40 @@ void flush_signals(struct task_struct *t
 	spin_unlock_irqrestore(&t->sighand->siglock, flags);
 }
 
+static void __flush_itimer_signals(struct sigpending *pending)
+{
+	sigset_t signal, retain;
+	struct sigqueue *q, *n;
+
+	signal = pending->signal;
+	sigemptyset(&retain);
+
+	list_for_each_entry_safe(q, n, &pending->list, list) {
+		int sig = q->info.si_signo;
+
+		if (likely(q->info.si_code != SI_TIMER)) {
+			sigaddset(&retain, sig);
+		} else {
+			sigdelset(&signal, sig);
+			list_del_init(&q->list);
+			__sigqueue_free(q);
+		}
+	}
+
+	sigorsets(&pending->signal, &signal, &retain);
+}
+
+void flush_itimer_signals(void)
+{
+	struct task_struct *tsk = current;
+	unsigned long flags;
+
+	spin_lock_irqsave(&tsk->sighand->siglock, flags);
+	__flush_itimer_signals(&tsk->pending);
+	__flush_itimer_signals(&tsk->signal->shared_pending);
+	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
+}
+
 void ignore_signals(struct task_struct *t)
 {
 	int i;

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