[PATCH] Simpler signal-exit concurrency handling

Some simplification in checking signal delivery against concurrent exit.
Instead of using get_task_struct_rcu(), which increments the task_struct
reference count, check the reference count after acquiring sighand lock.

Signed-off-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 64737c72dadd..9b6fda5e87f1 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1102,18 +1102,19 @@ int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
 
 retry:
         ret = check_kill_permission(sig, info, p);
-        if (!ret && sig && (sp = p->sighand)) {
-                if (!get_task_struct_rcu(p))
-                        return -ESRCH;
+        if (!ret && sig && (sp = rcu_dereference(p->sighand))) {
                 spin_lock_irqsave(&sp->siglock, flags);
                 if (p->sighand != sp) {
                         spin_unlock_irqrestore(&sp->siglock, flags);
-                        put_task_struct(p);
                         goto retry;
                 }
+                if ((atomic_read(&sp->count) == 0) ||
+                                (atomic_read(&p->usage) == 0)) {
+                        spin_unlock_irqrestore(&sp->siglock, flags);
+                        return -ESRCH;
+                }
                 ret = __group_send_sig_info(sig, info, p);
                 spin_unlock_irqrestore(&sp->siglock, flags);
-                put_task_struct(p);
         }
 
         return ret;