[PATCH] proc race on task_struct->sig

Originally from Chris Mason <mason@suse.com>..

collect_sigign_sigcatch can race against exit_sighand.  I haven't been
able to reproduce it, but I think it causes the oops reported in the
'Kernel Hangs 2.4.16 on heavy io Oracle Tivolie TSM' thread.

fs/proc/array.c

@@ -227,6 +227,7 @@ static void collect_sigign_sigcatch(struct task_struct *p, sigset_t *ign,
 	sigemptyset(ign);
 	sigemptyset(catch);
 
+	spin_lock_irq(&p->sigmask_lock);
 	if (p->sig) {
 		k = p->sig->action;
 		for (i = 1; i <= _NSIG; ++i, ++k) {
@@ -236,6 +237,7 @@ static void collect_sigign_sigcatch(struct task_struct *p, sigset_t *ign,
 				sigaddset(catch, i);
 		}
 	}
+	spin_unlock_irq(&p->sigmask_lock);
 }
 
 static inline char * task_sig(struct task_struct *p, char *buffer)