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Message-Id: <20080506003239.43FF026FA20@magilla.localdomain>
Date: Mon, 5 May 2008 17:32:39 -0700 (PDT)
From: Roland McGrath <roland@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] 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@...hat.com>
---
kernel/exit.c | 212 +++++++++++++++++++++++++++++++++++---------------------
1 files changed, 132 insertions(+), 80 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index 1510f78..934371a 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1232,7 +1232,7 @@ 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)
{
@@ -1240,7 +1240,10 @@ 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;
@@ -1391,13 +1394,16 @@ 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);
@@ -1415,7 +1421,7 @@ 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;
@@ -1436,7 +1442,7 @@ 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);
@@ -1470,7 +1476,7 @@ 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)
{
@@ -1478,6 +1484,9 @@ 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;
@@ -1487,7 +1496,7 @@ 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);
@@ -1513,89 +1522,134 @@ static int wait_task_continued(struct task_struct *p, int noreap,
return retval;
}
+/*
+ * Consider @p for a wait by @parent.
+ *
+ * -ECHILD should be in *@...val 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 *@...val 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 *retval,
+ 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.
+ */
+ *retval = 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 *@...val 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 *@...val is
+ * 0 if there were any eligible children, or still -ECHILD.
+ */
+static int do_wait_thread(struct task_struct *tsk, int *retval,
+ 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, retval, type, pid, options,
+ infop, stat_addr, ru);
+ if (ret)
+ return ret;
+ }
+
+ return 0;
+}
+
+static int ptrace_do_wait(struct task_struct *tsk, int *retval,
+ 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 *@...val if there are any,
+ * because we will eventually be allowed to wait for them again.
+ */
+ if (!*retval)
+ 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) {
+ *retval = 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(¤t->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 ret = do_wait_thread(tsk, &retval, type, pid, options,
+ infop, stat_addr, ru);
+ if (!ret)
+ ret = ptrace_do_wait(tsk, &retval, type, pid, options,
+ infop, stat_addr, ru);
+ if (ret) {
+ /*
+ * tasklist_lock is unlocked and we have a final result.
+ */
+ retval = ret;
+ goto end;
}
+
if (options & __WNOTHREAD)
break;
tsk = next_thread(tsk);
@@ -1603,16 +1657,14 @@ 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(¤t->signal->wait_chldexit,&wait);
--
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