wait_task_zombie: fix 2/3 races vs forget_original_parent()

[linux-2.6-block.git] / kernel / exit.c

diff --git a/kernel/exit.c b/kernel/exit.c
index 9d6e0897a4476dac387116af94aa721f06183219..b4d569675d4bd2881cbab0dc87893070e5318309 100644 (file)
--- 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;
 }