1 files changed, 21 insertions, 24 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 9d6e0897a447..b4d569675d4b 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1158,8 +1158,7 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
                             int __user *stat_addr, struct rusage __user *ru)
 {
         unsigned long state;
-        int retval;
-        int status;
+        int retval, status, traced;
 
         if (unlikely(noreap)) {
                 pid_t pid = p->pid;
@@ -1201,7 +1200,10 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
                 return 0;
         }
 
-        if (likely(p->real_parent == p->parent)) {
+        /* traced means p->ptrace, but not vice versa */
+        traced = (p->real_parent != p->parent);
+
+        if (likely(!traced)) {
                 struct signal_struct *psig;
                 struct signal_struct *sig;
 
@@ -1288,35 +1290,30 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
                 retval = put_user(p->pid, &infop->si_pid);
         if (!retval && infop)
                 retval = put_user(p->uid, &infop->si_uid);
-        if (retval) {
-                // TODO: is this safe?
-                p->exit_state = EXIT_ZOMBIE;
-                return retval;
-        }
-        retval = p->pid;
-        if (p->real_parent != p->parent) {
+        if (!retval)
+                retval = p->pid;
+
+        if (traced) {
                 write_lock_irq(&tasklist_lock);
-                /* Double-check with lock held.  */
-                if (p->real_parent != p->parent) {
-                        __ptrace_unlink(p);
-                        // TODO: is this safe?
-                        p->exit_state = EXIT_ZOMBIE;
-                        /*
-                         * If this is not a detached task, notify the parent.
-                         * If it's still not detached after that, don't release
-                         * it now.
-                         */
+                /* We dropped tasklist, ptracer could die and untrace */
+                ptrace_unlink(p);
+                /*
+                 * If this is not a detached task, notify the parent.
+                 * If it's still not detached after that, don't release
+                 * it now.
+                 */
+                if (p->exit_signal != -1) {
+                        do_notify_parent(p, p->exit_signal);
                         if (p->exit_signal != -1) {
-                                do_notify_parent(p, p->exit_signal);
-                                if (p->exit_signal != -1)
-                                        p = NULL;
+                                p->exit_state = EXIT_ZOMBIE;
+                                p = NULL;
                         }
                 }
                 write_unlock_irq(&tasklist_lock);
         }
         if (p != NULL)
                 release_task(p);
-        BUG_ON(!retval);
+
         return retval;
 }