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![Eric W. Biederman](/assets/img/avatar_default.png)
Currently there is a circular reference between work queue initialization and kthread initialization. This prevents the kthread infrastructure from initializing until after work queues have been initialized. We want the properties of tasks created with kthread_create to be as close as possible to the init_task and to not be contaminated by user processes. The later we start our kthreadd that creates these tasks the harder it is to avoid contamination from user processes and the more of a mess we have to clean up because the defaults have changed on us. So this patch modifies the kthread support to not use work queues but to instead use a simple list of structures, and to have kthreadd start from init_task immediately after our kernel thread that execs /sbin/init. By being a true child of init_task we only have to change those process settings that we want to have different from init_task, such as our process name, the cpus that are allowed, blocking all signals and setting SIGCHLD to SIG_IGN so that all of our children are reaped automatically. By being a true child of init_task we also naturally get our ppid set to 0 and do not wind up as a child of PID == 1. Ensuring that tasks generated by kthread_create will not slow down the functioning of the wait family of functions. [akpm@linux-foundation.org: use interruptible sleeps] Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
268 lines
7.1 KiB
C
268 lines
7.1 KiB
C
/* Kernel thread helper functions.
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* Copyright (C) 2004 IBM Corporation, Rusty Russell.
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*
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* Creation is done via kthreadd, so that we get a clean environment
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* even if we're invoked from userspace (think modprobe, hotplug cpu,
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* etc.).
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*/
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#include <linux/sched.h>
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#include <linux/kthread.h>
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#include <linux/completion.h>
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#include <linux/err.h>
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#include <linux/unistd.h>
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#include <linux/file.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <asm/semaphore.h>
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static DEFINE_SPINLOCK(kthread_create_lock);
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static LIST_HEAD(kthread_create_list);
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struct task_struct *kthreadd_task;
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struct kthread_create_info
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{
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/* Information passed to kthread() from kthreadd. */
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int (*threadfn)(void *data);
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void *data;
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struct completion started;
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/* Result passed back to kthread_create() from kthreadd. */
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struct task_struct *result;
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struct completion done;
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struct list_head list;
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};
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struct kthread_stop_info
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{
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struct task_struct *k;
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int err;
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struct completion done;
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};
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/* Thread stopping is done by setthing this var: lock serializes
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* multiple kthread_stop calls. */
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static DEFINE_MUTEX(kthread_stop_lock);
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static struct kthread_stop_info kthread_stop_info;
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/**
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* kthread_should_stop - should this kthread return now?
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*
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* When someone calls kthread_stop() on your kthread, it will be woken
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* and this will return true. You should then return, and your return
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* value will be passed through to kthread_stop().
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*/
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int kthread_should_stop(void)
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{
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return (kthread_stop_info.k == current);
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}
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EXPORT_SYMBOL(kthread_should_stop);
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static int kthread(void *_create)
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{
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struct kthread_create_info *create = _create;
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int (*threadfn)(void *data);
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void *data;
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int ret = -EINTR;
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/* Copy data: it's on kthread's stack */
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threadfn = create->threadfn;
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data = create->data;
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/* OK, tell user we're spawned, wait for stop or wakeup */
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__set_current_state(TASK_INTERRUPTIBLE);
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complete(&create->started);
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schedule();
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if (!kthread_should_stop())
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ret = threadfn(data);
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/* It might have exited on its own, w/o kthread_stop. Check. */
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if (kthread_should_stop()) {
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kthread_stop_info.err = ret;
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complete(&kthread_stop_info.done);
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}
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return 0;
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}
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static void create_kthread(struct kthread_create_info *create)
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{
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int pid;
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/* We want our own signal handler (we take no signals by default). */
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pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
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if (pid < 0) {
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create->result = ERR_PTR(pid);
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} else {
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wait_for_completion(&create->started);
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read_lock(&tasklist_lock);
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create->result = find_task_by_pid(pid);
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read_unlock(&tasklist_lock);
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}
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complete(&create->done);
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}
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/**
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* kthread_create - create a kthread.
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* @threadfn: the function to run until signal_pending(current).
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* @data: data ptr for @threadfn.
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* @namefmt: printf-style name for the thread.
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*
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* Description: This helper function creates and names a kernel
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* thread. The thread will be stopped: use wake_up_process() to start
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* it. See also kthread_run(), kthread_create_on_cpu().
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*
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* When woken, the thread will run @threadfn() with @data as its
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* argument. @threadfn() can either call do_exit() directly if it is a
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* standalone thread for which noone will call kthread_stop(), or
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* return when 'kthread_should_stop()' is true (which means
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* kthread_stop() has been called). The return value should be zero
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* or a negative error number; it will be passed to kthread_stop().
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*
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* Returns a task_struct or ERR_PTR(-ENOMEM).
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*/
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struct task_struct *kthread_create(int (*threadfn)(void *data),
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void *data,
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const char namefmt[],
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...)
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{
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struct kthread_create_info create;
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create.threadfn = threadfn;
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create.data = data;
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init_completion(&create.started);
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init_completion(&create.done);
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spin_lock(&kthread_create_lock);
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list_add_tail(&create.list, &kthread_create_list);
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wake_up_process(kthreadd_task);
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spin_unlock(&kthread_create_lock);
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wait_for_completion(&create.done);
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if (!IS_ERR(create.result)) {
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va_list args;
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va_start(args, namefmt);
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vsnprintf(create.result->comm, sizeof(create.result->comm),
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namefmt, args);
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va_end(args);
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}
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return create.result;
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}
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EXPORT_SYMBOL(kthread_create);
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/**
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* kthread_bind - bind a just-created kthread to a cpu.
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* @k: thread created by kthread_create().
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* @cpu: cpu (might not be online, must be possible) for @k to run on.
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*
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* Description: This function is equivalent to set_cpus_allowed(),
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* except that @cpu doesn't need to be online, and the thread must be
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* stopped (i.e., just returned from kthread_create()).
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*/
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void kthread_bind(struct task_struct *k, unsigned int cpu)
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{
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BUG_ON(k->state != TASK_INTERRUPTIBLE);
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/* Must have done schedule() in kthread() before we set_task_cpu */
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wait_task_inactive(k);
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set_task_cpu(k, cpu);
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k->cpus_allowed = cpumask_of_cpu(cpu);
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}
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EXPORT_SYMBOL(kthread_bind);
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/**
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* kthread_stop - stop a thread created by kthread_create().
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* @k: thread created by kthread_create().
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*
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* Sets kthread_should_stop() for @k to return true, wakes it, and
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* waits for it to exit. Your threadfn() must not call do_exit()
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* itself if you use this function! This can also be called after
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* kthread_create() instead of calling wake_up_process(): the thread
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* will exit without calling threadfn().
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*
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* Returns the result of threadfn(), or %-EINTR if wake_up_process()
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* was never called.
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*/
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int kthread_stop(struct task_struct *k)
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{
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int ret;
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mutex_lock(&kthread_stop_lock);
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/* It could exit after stop_info.k set, but before wake_up_process. */
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get_task_struct(k);
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/* Must init completion *before* thread sees kthread_stop_info.k */
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init_completion(&kthread_stop_info.done);
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smp_wmb();
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/* Now set kthread_should_stop() to true, and wake it up. */
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kthread_stop_info.k = k;
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wake_up_process(k);
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put_task_struct(k);
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/* Once it dies, reset stop ptr, gather result and we're done. */
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wait_for_completion(&kthread_stop_info.done);
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kthread_stop_info.k = NULL;
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ret = kthread_stop_info.err;
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mutex_unlock(&kthread_stop_lock);
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return ret;
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}
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EXPORT_SYMBOL(kthread_stop);
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static __init void kthreadd_setup(void)
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{
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struct task_struct *tsk = current;
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struct k_sigaction sa;
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sigset_t blocked;
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set_task_comm(tsk, "kthreadd");
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/* Block and flush all signals */
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sigfillset(&blocked);
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sigprocmask(SIG_BLOCK, &blocked, NULL);
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flush_signals(tsk);
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/* SIG_IGN makes children autoreap: see do_notify_parent(). */
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sa.sa.sa_handler = SIG_IGN;
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sa.sa.sa_flags = 0;
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siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
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do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
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set_user_nice(current, -5);
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set_cpus_allowed(current, CPU_MASK_ALL);
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}
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int kthreadd(void *unused)
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{
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/* Setup a clean context for our children to inherit. */
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kthreadd_setup();
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current->flags |= PF_NOFREEZE;
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for (;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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if (list_empty(&kthread_create_list))
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schedule();
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__set_current_state(TASK_RUNNING);
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spin_lock(&kthread_create_lock);
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while (!list_empty(&kthread_create_list)) {
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struct kthread_create_info *create;
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create = list_entry(kthread_create_list.next,
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struct kthread_create_info, list);
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list_del_init(&create->list);
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spin_unlock(&kthread_create_lock);
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create_kthread(create);
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spin_lock(&kthread_create_lock);
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}
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spin_unlock(&kthread_create_lock);
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}
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return 0;
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}
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