1 files changed, 25 insertions, 17 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 8f0876f9f6dd..19e35135fc60 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1275,7 +1275,17 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
                         local_irq_restore(*flags);
                         break;
                 }
-
+                /*
+                 * This sighand can be already freed and even reused, but
+                 * we rely on SLAB_DESTROY_BY_RCU and sighand_ctor() which
+                 * initializes ->siglock: this slab can't go away, it has
+                 * the same object type, ->siglock can't be reinitialized.
+                 *
+                 * We need to ensure that tsk->sighand is still the same
+                 * after we take the lock, we can race with de_thread() or
+                 * __exit_signal(). In the latter case the next iteration
+                 * must see ->sighand == NULL.
+                 */
                 spin_lock(&sighand->siglock);
                 if (likely(sighand == tsk->sighand)) {
                         rcu_read_unlock();
@@ -1331,23 +1341,21 @@ int kill_pid_info(int sig, struct siginfo *info, struct pid *pid)
         int error = -ESRCH;
         struct task_struct *p;
 
-        rcu_read_lock();
-retry:
-        p = pid_task(pid, PIDTYPE_PID);
-        if (p) {
-                error = group_send_sig_info(sig, info, p);
-                if (unlikely(error == -ESRCH))
-                        /*
-                         * The task was unhashed in between, try again.
-                         * If it is dead, pid_task() will return NULL,
-                         * if we race with de_thread() it will find the
-                         * new leader.
-                         */
-                        goto retry;
-        }
-        rcu_read_unlock();
+        for (;;) {
+                rcu_read_lock();
+                p = pid_task(pid, PIDTYPE_PID);
+                if (p)
+                        error = group_send_sig_info(sig, info, p);
+                rcu_read_unlock();
+                if (likely(!p || error != -ESRCH))
+                        return error;
 
-        return error;
+                /*
+                 * The task was unhashed in between, try again.  If it
+                 * is dead, pid_task() will return NULL, if we race with
+                 * de_thread() it will find the new leader.
+                 */
+        }
 }
 
 int kill_proc_info(int sig, struct siginfo *info, pid_t pid)