It's a shame kthread_stop() (may take a while!) runs with a global semaphore
held. With this patch kthread() allocates all neccesary data (struct kthread)
on its own stack, globals kthread_stop_xxx are deleted.
HACKS:
- re-use task_struct->set_child_tid to point to "struct kthread"
- use do_exit() directly to preserve "struct kthread" on stack
Signed-off-by: Oleg Nesterov <[email protected]>
--- 2.6.21-rc5/kernel/kthread.c~3_STOP 2007-04-13 16:28:41.000000000 +0400
+++ 2.6.21-rc5/kernel/kthread.c 2007-04-13 16:24:37.000000000 +0400
@@ -17,7 +17,25 @@
static DEFINE_SPINLOCK(kthread_create_lock);
static LIST_HEAD(kthread_create_list);
-struct task_struct *kthreadd_task;
+struct task_struct *kthreadd_task __read_mostly;
+
+struct kthread {
+ int should_stop;
+ struct task_struct *task;
+
+ struct completion exited;
+ int err;
+};
+
+static inline struct kthread *to_kthread(struct task_struct *t)
+{
+ return (void*)t->set_child_tid;
+}
+
+static inline void set_kthread(struct kthread *self)
+{
+ current->set_child_tid = (void __user*)self;
+}
struct kthread_create_info
{
@@ -27,24 +45,12 @@ struct kthread_create_info
struct completion created;
struct completion started;
- /* Result passed back to kthread_create() from kthreadd. */
- pid_t result;
+ /* Result passed back to kthread_create() from kthread. */
+ struct kthread *result;
struct list_head list;
};
-struct kthread_stop_info
-{
- struct task_struct *k;
- int err;
- struct completion done;
-};
-
-/* Thread stopping is done by setthing this var: lock serializes
- * multiple kthread_stop calls. */
-static DEFINE_MUTEX(kthread_stop_lock);
-static struct kthread_stop_info kthread_stop_info;
-
/**
* kthread_should_stop - should this kthread return now?
*
@@ -54,20 +60,28 @@ static struct kthread_stop_info kthread_
*/
int kthread_should_stop(void)
{
- return (kthread_stop_info.k == current);
+ return to_kthread(current)->should_stop;
}
EXPORT_SYMBOL(kthread_should_stop);
static int kthread(void *_create)
{
- struct kthread_create_info *create = _create;
- int (*threadfn)(void *data);
- void *data;
- int ret = -EINTR;
+ struct kthread self = {
+ .task = current,
+ .err = -EINTR,
+ };
/* Copy data: it's on kthread's stack */
- threadfn = create->threadfn;
- data = create->data;
+ struct kthread_create_info *create = _create;
+ int (*threadfn)(void *data) = create->threadfn;
+ void *data = create->data;
+
+ /*
+ * This should be enough to assure that self is still on
+ * stack when we enter do_exit()
+ */
+ set_kthread(&self);
+ create->result = &self;
/* OK, tell user we're spawned, wait for stop or wakeup */
__set_current_state(TASK_UNINTERRUPTIBLE);
@@ -75,13 +89,13 @@ static int kthread(void *_create)
schedule();
if (!kthread_should_stop())
- ret = threadfn(data);
+ self.err = threadfn(data);
- /* It might have exited on its own, w/o kthread_stop. Check. */
- if (kthread_should_stop()) {
- kthread_stop_info.err = ret;
- complete(&kthread_stop_info.done);
- }
+ /* It might have exited on its own, w/o kthread_stop. Check. */
+ if (kthread_should_stop())
+ complete(&self.exited);
+
+ do_exit(0);
return 0;
}
@@ -91,7 +105,7 @@ 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);
- create->result = pid;
+ create->result = ERR_PTR(pid);
complete(&create->created);
}
@@ -135,11 +149,11 @@ struct task_struct *kthread_create(int (
wake_up_process(kthreadd_task);
wait_for_completion(&create.created);
- if (create.result < 0)
- return ERR_PTR(create.result);
+ if (IS_ERR(create.result))
+ return (void*)create.result;
wait_for_completion(&create.started);
- ret = find_task_by_pid(create.result);
+ ret = create.result->task;
va_start(args, namefmt);
vsnprintf(ret->comm, sizeof(ret->comm), namefmt, args);
@@ -183,27 +197,23 @@ EXPORT_SYMBOL(kthread_bind);
*/
int kthread_stop(struct task_struct *k)
{
+ struct kthread *kthread;
int ret;
- mutex_lock(&kthread_stop_lock);
-
/* It could exit after stop_info.k set, but before wake_up_process. */
get_task_struct(k);
+ kthread = to_kthread(k);
- /* Must init completion *before* thread sees kthread_stop_info.k */
- init_completion(&kthread_stop_info.done);
+ /* Must init completion *before* thread sees ->should_stop */
+ init_completion(&kthread->exited);
smp_wmb();
-
- /* Now set kthread_should_stop() to true, and wake it up. */
- kthread_stop_info.k = k;
+ kthread->should_stop = 1;
wake_up_process(k);
- put_task_struct(k);
/* Once it dies, reset stop ptr, gather result and we're done. */
- wait_for_completion(&kthread_stop_info.done);
- kthread_stop_info.k = NULL;
- ret = kthread_stop_info.err;
- mutex_unlock(&kthread_stop_lock);
+ wait_for_completion(&kthread->exited);
+ ret = kthread->err;
+ put_task_struct(k);
return ret;
}
-
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