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linux-next/kernel/kthread.c
David Howells 65f27f3844 WorkStruct: Pass the work_struct pointer instead of context data
Pass the work_struct pointer to the work function rather than context data.
The work function can use container_of() to work out the data.

For the cases where the container of the work_struct may go away the moment the
pending bit is cleared, it is made possible to defer the release of the
structure by deferring the clearing of the pending bit.

To make this work, an extra flag is introduced into the management side of the
work_struct.  This governs auto-release of the structure upon execution.

Ordinarily, the work queue executor would release the work_struct for further
scheduling or deallocation by clearing the pending bit prior to jumping to the
work function.  This means that, unless the driver makes some guarantee itself
that the work_struct won't go away, the work function may not access anything
else in the work_struct or its container lest they be deallocated..  This is a
problem if the auxiliary data is taken away (as done by the last patch).

However, if the pending bit is *not* cleared before jumping to the work
function, then the work function *may* access the work_struct and its container
with no problems.  But then the work function must itself release the
work_struct by calling work_release().

In most cases, automatic release is fine, so this is the default.  Special
initiators exist for the non-auto-release case (ending in _NAR).


Signed-Off-By: David Howells <dhowells@redhat.com>
2006-11-22 14:55:48 +00:00

257 lines
6.8 KiB
C

/* Kernel thread helper functions.
* Copyright (C) 2004 IBM Corporation, Rusty Russell.
*
* Creation is done via keventd, so that we get a clean environment
* even if we're invoked from userspace (think modprobe, hotplug cpu,
* etc.).
*/
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/unistd.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <asm/semaphore.h>
/*
* We dont want to execute off keventd since it might
* hold a semaphore our callers hold too:
*/
static struct workqueue_struct *helper_wq;
struct kthread_create_info
{
/* Information passed to kthread() from keventd. */
int (*threadfn)(void *data);
void *data;
struct completion started;
/* Result passed back to kthread_create() from keventd. */
struct task_struct *result;
struct completion done;
struct work_struct work;
};
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?
*
* When someone calls kthread_stop on your kthread, it will be woken
* and this will return true. You should then return, and your return
* value will be passed through to kthread_stop().
*/
int kthread_should_stop(void)
{
return (kthread_stop_info.k == current);
}
EXPORT_SYMBOL(kthread_should_stop);
static void kthread_exit_files(void)
{
struct fs_struct *fs;
struct task_struct *tsk = current;
exit_fs(tsk); /* current->fs->count--; */
fs = init_task.fs;
tsk->fs = fs;
atomic_inc(&fs->count);
exit_files(tsk);
current->files = init_task.files;
atomic_inc(&tsk->files->count);
}
static int kthread(void *_create)
{
struct kthread_create_info *create = _create;
int (*threadfn)(void *data);
void *data;
sigset_t blocked;
int ret = -EINTR;
kthread_exit_files();
/* Copy data: it's on keventd's stack */
threadfn = create->threadfn;
data = create->data;
/* Block and flush all signals (in case we're not from keventd). */
sigfillset(&blocked);
sigprocmask(SIG_BLOCK, &blocked, NULL);
flush_signals(current);
/* By default we can run anywhere, unlike keventd. */
set_cpus_allowed(current, CPU_MASK_ALL);
/* OK, tell user we're spawned, wait for stop or wakeup */
__set_current_state(TASK_INTERRUPTIBLE);
complete(&create->started);
schedule();
if (!kthread_should_stop())
ret = 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);
}
return 0;
}
/* We are keventd: create a thread. */
static void keventd_create_kthread(struct work_struct *work)
{
struct kthread_create_info *create =
container_of(work, struct kthread_create_info, work);
int pid;
/* 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);
}
/**
* kthread_create - create a kthread.
* @threadfn: the function to run until signal_pending(current).
* @data: data ptr for @threadfn.
* @namefmt: printf-style name for the thread.
*
* Description: This helper function creates and names a kernel
* thread. The thread will be stopped: use wake_up_process() to start
* it. See also kthread_run(), kthread_create_on_cpu().
*
* When woken, the thread will run @threadfn() with @data as its
* argument. @threadfn can either call do_exit() directly if it is a
* standalone thread for which noone will call kthread_stop(), or
* return when 'kthread_should_stop()' is true (which means
* kthread_stop() has been called). The return value should be zero
* or a negative error number; it will be passed to kthread_stop().
*
* Returns a task_struct or ERR_PTR(-ENOMEM).
*/
struct task_struct *kthread_create(int (*threadfn)(void *data),
void *data,
const char namefmt[],
...)
{
struct kthread_create_info create;
create.threadfn = threadfn;
create.data = data;
init_completion(&create.started);
init_completion(&create.done);
INIT_WORK(&create.work, keventd_create_kthread);
/*
* The workqueue needs to start up first:
*/
if (!helper_wq)
create.work.func(&create.work);
else {
queue_work(helper_wq, &create.work);
wait_for_completion(&create.done);
}
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;
}
EXPORT_SYMBOL(kthread_create);
/**
* kthread_bind - bind a just-created kthread to a cpu.
* @k: thread created by kthread_create().
* @cpu: cpu (might not be online, must be possible) for @k to run on.
*
* Description: This function is equivalent to set_cpus_allowed(),
* except that @cpu doesn't need to be online, and the thread must be
* stopped (i.e., just returned from kthread_create().
*/
void kthread_bind(struct task_struct *k, unsigned int cpu)
{
BUG_ON(k->state != TASK_INTERRUPTIBLE);
/* Must have done schedule() in kthread() before we set_task_cpu */
wait_task_inactive(k);
set_task_cpu(k, cpu);
k->cpus_allowed = cpumask_of_cpu(cpu);
}
EXPORT_SYMBOL(kthread_bind);
/**
* kthread_stop - stop a thread created by kthread_create().
* @k: thread created by kthread_create().
*
* Sets kthread_should_stop() for @k to return true, wakes it, and
* waits for it to exit. Your threadfn() must not call do_exit()
* itself if you use this function! This can also be called after
* kthread_create() instead of calling wake_up_process(): the thread
* will exit without calling threadfn().
*
* Returns the result of threadfn(), or %-EINTR if wake_up_process()
* was never called.
*/
int kthread_stop(struct task_struct *k)
{
int ret;
mutex_lock(&kthread_stop_lock);
/* It could exit after stop_info.k set, but before wake_up_process. */
get_task_struct(k);
/* Must init completion *before* thread sees kthread_stop_info.k */
init_completion(&kthread_stop_info.done);
smp_wmb();
/* Now set kthread_should_stop() to true, and wake it up. */
kthread_stop_info.k = k;
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);
return ret;
}
EXPORT_SYMBOL(kthread_stop);
static __init int helper_init(void)
{
helper_wq = create_singlethread_workqueue("kthread");
BUG_ON(!helper_wq);
return 0;
}
core_initcall(helper_init);