If kernel_thread(kthread) succeeds, kthread() can not fail on its path to
complete(&create->started) + schedule(). After that it can't be woken because
nobody can see the new task yet. This means:
- we don't need tasklist_lock for find_task_by_pid().
- create_kthread() doesn't need to wait for create->started. Instead,
kthread_create() first waits for create->created to get the result of
kernel_thread(), then waits for create->started to synchronize with
kthread().
Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>
--- 2.6.21-rc5/kernel/kthread.c~1_CREATE 2007-04-13 14:39:21.000000000
+0400
+++ 2.6.21-rc5/kernel/kthread.c 2007-04-13 14:52:44.000000000 +0400
@@ -24,11 +24,11 @@ struct kthread_create_info
/* Information passed to kthread() from kthreadd. */
int (*threadfn)(void *data);
void *data;
+ struct completion created;
struct completion started;
/* Result passed back to kthread_create() from kthreadd. */
- struct task_struct *result;
- struct completion done;
+ pid_t result;
struct list_head list;
};
@@ -91,15 +91,9 @@ static void create_kthread(struct kthrea
/* We want our own signal handler (we take no signals by default). */
pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
- if (pid < 0) {
- create->result = ERR_PTR(pid);
- } else {
- wait_for_completion(&create->started);
- read_lock(&tasklist_lock);
- create->result = find_task_by_pid(pid);
- read_unlock(&tasklist_lock);
- }
- complete(&create->done);
+ create->result = pid;
+
+ complete(&create->created);
}
/**
@@ -127,27 +121,31 @@ struct task_struct *kthread_create(int (
...)
{
struct kthread_create_info create;
+ struct task_struct *ret;
+ va_list args;
create.threadfn = threadfn;
create.data = data;
+ init_completion(&create.created);
init_completion(&create.started);
- init_completion(&create.done);
spin_lock(&kthread_create_lock);
list_add_tail(&create.list, &kthread_create_list);
- wake_up_process(kthreadd_task);
spin_unlock(&kthread_create_lock);
+ wake_up_process(kthreadd_task);
- wait_for_completion(&create.done);
+ wait_for_completion(&create.created);
+ if (create.result < 0)
+ return ERR_PTR(create.result);
- if (!IS_ERR(create.result)) {
- va_list args;
- va_start(args, namefmt);
- vsnprintf(create.result->comm, sizeof(create.result->comm),
- namefmt, args);
- va_end(args);
- }
- return create.result;
+ wait_for_completion(&create.started);
+ ret = find_task_by_pid(create.result);
+
+ va_start(args, namefmt);
+ vsnprintf(ret->comm, sizeof(ret->comm), namefmt, args);
+ va_end(args);
+
+ return ret;
}
EXPORT_SYMBOL(kthread_create);
-
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