do_wait reorganization
authorRoland McGrath <roland@redhat.com>
Thu, 20 Mar 2008 02:24:59 +0000 (19:24 -0700)
committerRoland McGrath <roland@redhat.com>
Thu, 17 Jul 2008 01:02:33 +0000 (18:02 -0700)
This breaks out the guts of do_wait into three subfunctions.
The control flow is less nonobvious without so much goto.
do_wait_thread and ptrace_do_wait contain the main work of the outer loop.
wait_consider_task contains the main work of the inner loop.

Signed-off-by: Roland McGrath <roland@redhat.com>
kernel/exit.c

index ceb258782835a1073774e0337e0bc4d85f7a160f..7453356a961f7fa5fb3e6e1f8c8a666c8487cb25 100644 (file)
@@ -1238,7 +1238,7 @@ static int wait_noreap_copyout(struct task_struct *p, pid_t pid, uid_t uid,
  * the lock and this task is uninteresting.  If we return nonzero, we have
  * released the lock and the system call should return.
  */
-static int wait_task_zombie(struct task_struct *p, int noreap,
+static int wait_task_zombie(struct task_struct *p, int options,
                            struct siginfo __user *infop,
                            int __user *stat_addr, struct rusage __user *ru)
 {
@@ -1246,7 +1246,10 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
        int retval, status, traced;
        pid_t pid = task_pid_vnr(p);
 
-       if (unlikely(noreap)) {
+       if (!likely(options & WEXITED))
+               return 0;
+
+       if (unlikely(options & WNOWAIT)) {
                uid_t uid = p->uid;
                int exit_code = p->exit_code;
                int why, status;
@@ -1397,13 +1400,16 @@ static int wait_task_zombie(struct task_struct *p, int noreap,
  * released the lock and the system call should return.
  */
 static int wait_task_stopped(struct task_struct *p,
-                            int noreap, struct siginfo __user *infop,
+                            int options, struct siginfo __user *infop,
                             int __user *stat_addr, struct rusage __user *ru)
 {
        int retval, exit_code, why;
        uid_t uid = 0; /* unneeded, required by compiler */
        pid_t pid;
 
+       if (!(p->ptrace & PT_PTRACED) && !(options & WUNTRACED))
+               return 0;
+
        exit_code = 0;
        spin_lock_irq(&p->sighand->siglock);
 
@@ -1421,7 +1427,7 @@ static int wait_task_stopped(struct task_struct *p,
        if (!exit_code)
                goto unlock_sig;
 
-       if (!noreap)
+       if (!unlikely(options & WNOWAIT))
                p->exit_code = 0;
 
        uid = p->uid;
@@ -1442,7 +1448,7 @@ unlock_sig:
        why = (p->ptrace & PT_PTRACED) ? CLD_TRAPPED : CLD_STOPPED;
        read_unlock(&tasklist_lock);
 
-       if (unlikely(noreap))
+       if (unlikely(options & WNOWAIT))
                return wait_noreap_copyout(p, pid, uid,
                                           why, exit_code,
                                           infop, ru);
@@ -1476,7 +1482,7 @@ unlock_sig:
  * the lock and this task is uninteresting.  If we return nonzero, we have
  * released the lock and the system call should return.
  */
-static int wait_task_continued(struct task_struct *p, int noreap,
+static int wait_task_continued(struct task_struct *p, int options,
                               struct siginfo __user *infop,
                               int __user *stat_addr, struct rusage __user *ru)
 {
@@ -1484,6 +1490,9 @@ static int wait_task_continued(struct task_struct *p, int noreap,
        pid_t pid;
        uid_t uid;
 
+       if (!unlikely(options & WCONTINUED))
+               return 0;
+
        if (!(p->signal->flags & SIGNAL_STOP_CONTINUED))
                return 0;
 
@@ -1493,7 +1502,7 @@ static int wait_task_continued(struct task_struct *p, int noreap,
                spin_unlock_irq(&p->sighand->siglock);
                return 0;
        }
-       if (!noreap)
+       if (!unlikely(options & WNOWAIT))
                p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
        spin_unlock_irq(&p->sighand->siglock);
 
@@ -1519,89 +1528,137 @@ static int wait_task_continued(struct task_struct *p, int noreap,
        return retval;
 }
 
+/*
+ * Consider @p for a wait by @parent.
+ *
+ * -ECHILD should be in *@notask_error before the first call.
+ * Returns nonzero for a final return, when we have unlocked tasklist_lock.
+ * Returns zero if the search for a child should continue;
+ * then *@notask_error is 0 if @p is an eligible child, or still -ECHILD.
+ */
+static int wait_consider_task(struct task_struct *parent,
+                             struct task_struct *p, int *notask_error,
+                             enum pid_type type, struct pid *pid, int options,
+                             struct siginfo __user *infop,
+                             int __user *stat_addr, struct rusage __user *ru)
+{
+       int ret = eligible_child(type, pid, options, p);
+       if (ret <= 0)
+               return ret;
+
+       if (p->exit_state == EXIT_DEAD)
+               return 0;
+
+       /*
+        * We don't reap group leaders with subthreads.
+        */
+       if (p->exit_state == EXIT_ZOMBIE && !delay_group_leader(p))
+               return wait_task_zombie(p, options, infop, stat_addr, ru);
+
+       /*
+        * It's stopped or running now, so it might
+        * later continue, exit, or stop again.
+        */
+       *notask_error = 0;
+
+       if (task_is_stopped_or_traced(p))
+               return wait_task_stopped(p, options, infop, stat_addr, ru);
+
+       return wait_task_continued(p, options, infop, stat_addr, ru);
+}
+
+/*
+ * Do the work of do_wait() for one thread in the group, @tsk.
+ *
+ * -ECHILD should be in *@notask_error before the first call.
+ * Returns nonzero for a final return, when we have unlocked tasklist_lock.
+ * Returns zero if the search for a child should continue; then
+ * *@notask_error is 0 if there were any eligible children, or still -ECHILD.
+ */
+static int do_wait_thread(struct task_struct *tsk, int *notask_error,
+                         enum pid_type type, struct pid *pid, int options,
+                         struct siginfo __user *infop, int __user *stat_addr,
+                         struct rusage __user *ru)
+{
+       struct task_struct *p;
+
+       list_for_each_entry(p, &tsk->children, sibling) {
+               int ret = wait_consider_task(tsk, p, notask_error,
+                                            type, pid, options,
+                                            infop, stat_addr, ru);
+               if (ret)
+                       return ret;
+       }
+
+       return 0;
+}
+
+static int ptrace_do_wait(struct task_struct *tsk, int *notask_error,
+                         enum pid_type type, struct pid *pid, int options,
+                         struct siginfo __user *infop, int __user *stat_addr,
+                         struct rusage __user *ru)
+{
+       struct task_struct *p;
+
+       /*
+        * If we never saw an eligile child, check for children stolen by
+        * ptrace.  We don't leave -ECHILD in *@notask_error if there are any,
+        * because we will eventually be allowed to wait for them again.
+        */
+       if (!*notask_error)
+               return 0;
+
+       list_for_each_entry(p, &tsk->ptrace_children, ptrace_list) {
+               int ret = eligible_child(type, pid, options, p);
+               if (unlikely(ret < 0))
+                       return ret;
+               if (ret) {
+                       *notask_error = 0;
+                       return 0;
+               }
+       }
+
+       return 0;
+}
+
 static long do_wait(enum pid_type type, struct pid *pid, int options,
                    struct siginfo __user *infop, int __user *stat_addr,
                    struct rusage __user *ru)
 {
        DECLARE_WAITQUEUE(wait, current);
        struct task_struct *tsk;
-       int flag, retval;
+       int retval;
 
        add_wait_queue(&current->signal->wait_chldexit,&wait);
 repeat:
-       /* If there is nothing that can match our critier just get out */
+       /*
+        * If there is nothing that can match our critiera just get out.
+        * We will clear @retval to zero if we see any child that might later
+        * match our criteria, even if we are not able to reap it yet.
+        */
        retval = -ECHILD;
        if ((type < PIDTYPE_MAX) && (!pid || hlist_empty(&pid->tasks[type])))
                goto end;
 
-       /*
-        * We will set this flag if we see any child that might later
-        * match our criteria, even if we are not able to reap it yet.
-        */
-       flag = retval = 0;
        current->state = TASK_INTERRUPTIBLE;
        read_lock(&tasklist_lock);
        tsk = current;
        do {
-               struct task_struct *p;
-
-               list_for_each_entry(p, &tsk->children, sibling) {
-                       int ret = eligible_child(type, pid, options, p);
-                       if (!ret)
-                               continue;
-
-                       if (unlikely(ret < 0)) {
-                               retval = ret;
-                       } else if (task_is_stopped_or_traced(p)) {
-                               /*
-                                * It's stopped now, so it might later
-                                * continue, exit, or stop again.
-                                */
-                               flag = 1;
-                               if (!(p->ptrace & PT_PTRACED) &&
-                                   !(options & WUNTRACED))
-                                       continue;
-
-                               retval = wait_task_stopped(p,
-                                               (options & WNOWAIT), infop,
-                                               stat_addr, ru);
-                       } else if (p->exit_state == EXIT_ZOMBIE &&
-                                       !delay_group_leader(p)) {
-                               /*
-                                * We don't reap group leaders with subthreads.
-                                */
-                               if (!likely(options & WEXITED))
-                                       continue;
-                               retval = wait_task_zombie(p,
-                                               (options & WNOWAIT), infop,
-                                               stat_addr, ru);
-                       } else if (p->exit_state != EXIT_DEAD) {
-                               /*
-                                * It's running now, so it might later
-                                * exit, stop, or stop and then continue.
-                                */
-                               flag = 1;
-                               if (!unlikely(options & WCONTINUED))
-                                       continue;
-                               retval = wait_task_continued(p,
-                                               (options & WNOWAIT), infop,
-                                               stat_addr, ru);
-                       }
-                       if (retval != 0) /* tasklist_lock released */
-                               goto end;
-               }
-               if (!flag) {
-                       list_for_each_entry(p, &tsk->ptrace_children,
-                                                               ptrace_list) {
-                               flag = eligible_child(type, pid, options, p);
-                               if (!flag)
-                                       continue;
-                               if (likely(flag > 0))
-                                       break;
-                               retval = flag;
-                               goto end;
-                       }
+               int tsk_result = do_wait_thread(tsk, &retval,
+                                               type, pid, options,
+                                               infop, stat_addr, ru);
+               if (!tsk_result)
+                       tsk_result = ptrace_do_wait(tsk, &retval,
+                                                   type, pid, options,
+                                                   infop, stat_addr, ru);
+               if (tsk_result) {
+                       /*
+                        * tasklist_lock is unlocked and we have a final result.
+                        */
+                       retval = tsk_result;
+                       goto end;
                }
+
                if (options & __WNOTHREAD)
                        break;
                tsk = next_thread(tsk);
@@ -1609,16 +1666,14 @@ repeat:
        } while (tsk != current);
        read_unlock(&tasklist_lock);
 
-       if (flag) {
-               if (options & WNOHANG)
-                       goto end;
+       if (!retval && !(options & WNOHANG)) {
                retval = -ERESTARTSYS;
-               if (signal_pending(current))
-                       goto end;
-               schedule();
-               goto repeat;
+               if (!signal_pending(current)) {
+                       schedule();
+                       goto repeat;
+               }
        }
-       retval = -ECHILD;
+
 end:
        current->state = TASK_RUNNING;
        remove_wait_queue(&current->signal->wait_chldexit,&wait);