Unexpected lockups in scheduler with 2.5.60-2.5.69

Hi Linus,
there is problem with send_sig_info. This function can be invoked from
timer interrupt (timer_interrpt -> do_timer -> update_process_times -> -> update_one_process -> ( do_process_times, do_it_prof, do_it_virt ) -> -> send_sig -> send_sig_info) but it uses spin_unlock_irq instead of correct spin_unlock_irqrestore.

This enables interrupts, and later scheduler_tick() locks runqueue
(without disabling interrupts). And if we are unlucky, new interrupt comes at this point. And if this interrupt tries to do wake_up() (like RTC interrupt does), we deadlock on runqueue lock :-( And it is bad...

Problem was introduced by signal-fixes-2.5.59-A4, which spilt
original send_sig_info into two functions, and in one branch it started using these unsafe spinlock variants (while group variant uses irqsave/restore correctly).
Best regards,
Petr Vandrovec

diff -urdN linux/kernel/signal.c linux/kernel/signal.c
@@ -1145,6 +1145,7 @@
 int
 send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
 {
+	unsigned long flags;
 	int ret;
 
 	/*

@@ -1154,9 +1155,9 @@
 	 * going away or changing from under us.
 	 */
 	read_lock(&tasklist_lock);  
-	spin_lock_irq(&p->sighand->siglock);
+	spin_lock_irqsave(&p->sighand->siglock, flags);
 	ret = specific_send_sig_info(sig, info, p);
-	spin_unlock_irq(&p->sighand->siglock);
+	spin_unlock_irqrestore(&p->sighand->siglock, flags);
 	read_unlock(&tasklist_lock);
 	return ret;
 }