do_wait reorganization

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>

1 files changed, 135 insertions, 80 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index ceb258782835..7453356a961f 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -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);