From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266106AbTLaEUb (ORCPT ); Tue, 30 Dec 2003 23:20:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266109AbTLaEUa (ORCPT ); Tue, 30 Dec 2003 23:20:30 -0500 Received: from dp.samba.org ([66.70.73.150]:12442 "EHLO lists.samba.org") by vger.kernel.org with ESMTP id S266106AbTLaEUT (ORCPT ); Tue, 30 Dec 2003 23:20:19 -0500 From: Rusty Russell To: torvalds@osdl.org, akpm@osdl.org Cc: mingo@redhat.com, linux-kernel@vger.kernel.org Subject: [PATCH 1/2] kthread_create Date: Wed, 31 Dec 2003 14:31:08 +1100 Message-Id: <20031231042016.958DC2C04B@lists.samba.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi all, Ingo read through this before and liked it: this is the basis of the Hotplug CPU patch, and as such has been stressed fairly well. Tested stand-alone, and included here for wider review. Feedback welcome! Rusty. -- Anyone who quotes me in their sig is an idiot. -- Rusty Russell. Name: Kernel Thread Control Primitives Author: Rusty Russell Status: Tested on 2.6.0-bk3 D: The hotplug CPU code introduces two major problems: D: D: 1) Threads which previously never stopped (migration thread, D: ksoftirqd, keventd) have to be stopped cleanly as CPUs go offline. D: 2) Threads which previously never had to be created now have D: to be created when a CPU goes online. D: D: Unfortunately, stopping a thread is fairly baroque, involving memory D: barriers, a completion and spinning until the task is actually dead. D: D: There are also three problems in starting a thread: D: 1) Doing it from a random process context risks environment contamination: D: better to do it from keventd to guarantee a clean environment, a-la D: call_usermodehelper. D: 2) Getting the task struct without races is a hard: see kernel/sched.c D: migration_call(), kernel/workqueue.c create_workqueue_thread(). D: 3) There are races in starting a thread for a CPU which is not yet D: online: migration thread does a complex dance at the moment for D: a similar reason (there may be no migration thread to migrate us). D: D: Place all this logic in some primitives to make life easier: D: kthread_create(), kthread_start() and kthread_destroy(). These D: primitives require no extra data-structures in the caller: they operate D: on normal "struct task_struct"s. D: D: Other changes: D: - Expose keventd_up(), as keventd and migration threads will use D: kthread to launch, and kthread normally uses workqueues and must D: recognize this case. diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .32392-linux-2.6.0-test11-bk6/include/linux/kthread.h .32392-linux-2.6.0-test11-bk6.updated/include/linux/kthread.h --- .32392-linux-2.6.0-test11-bk6/include/linux/kthread.h 1970-01-01 10:00:00.000000000 +1000 +++ .32392-linux-2.6.0-test11-bk6.updated/include/linux/kthread.h 2003-12-09 17:42:29.000000000 +1100 @@ -0,0 +1,38 @@ +#ifndef _LINUX_KTHREAD_H +#define _LINUX_KTHREAD_H +/* Simple abstraction for kernel thread usage: the initfn is called at + * the start, if that's successful (ie. returns 0), then the thread + * sleeps. + * + * Every time the thread is woken, it will run corefn, until that + * returns an error. The thread must be ended by calling + * kthread_destroy(). + */ +#include +struct task_struct; + +/* Part I: create a kthread: if fork fails return ERR_PTR(-errno). */ +struct task_struct *kthread_create(int (*initfn)(void *data), + int (*corefn)(void *data), + void *data, + const char namefmt[], ...); + +/* Part II: have thread call initfn(); return thread if successful, + otherwise ERR_PTR(-errno). */ +struct task_struct *kthread_start(struct task_struct *k); + +/* Convenient wrapper for both of the above. */ +#define kthread_run(initfn, corefn, data, namefmt, ...) \ +({ \ + struct task_struct *__k \ + = kthread_create(initfn,corefn,data,namefmt, ## __VA_ARGS__); \ + if (!IS_ERR(__k)) \ + __k = kthread_start(__k); \ + __k; \ +}) + +/* Stop the thread. Return value is last return of corefn() (ie. zero + * if exited as normal). Can be called before kthread_start(). */ +int kthread_destroy(struct task_struct *k); + +#endif /* _LINUX_KTHREAD_H */ diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .32392-linux-2.6.0-test11-bk6/include/linux/workqueue.h .32392-linux-2.6.0-test11-bk6.updated/include/linux/workqueue.h --- .32392-linux-2.6.0-test11-bk6/include/linux/workqueue.h 2003-09-22 10:07:08.000000000 +1000 +++ .32392-linux-2.6.0-test11-bk6.updated/include/linux/workqueue.h 2003-12-09 17:42:29.000000000 +1100 @@ -60,6 +60,7 @@ extern int FASTCALL(schedule_work(struct extern int FASTCALL(schedule_delayed_work(struct work_struct *work, unsigned long delay)); extern void flush_scheduled_work(void); extern int current_is_keventd(void); +extern int keventd_up(void); extern void init_workqueues(void); diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .32392-linux-2.6.0-test11-bk6/kernel/Makefile .32392-linux-2.6.0-test11-bk6.updated/kernel/Makefile --- .32392-linux-2.6.0-test11-bk6/kernel/Makefile 2003-10-09 18:03:02.000000000 +1000 +++ .32392-linux-2.6.0-test11-bk6.updated/kernel/Makefile 2003-12-09 17:42:29.000000000 +1100 @@ -6,7 +6,8 @@ obj-y = sched.o fork.o exec_domain.o exit.o itimer.o time.o softirq.o resource.o \ sysctl.o capability.o ptrace.o timer.o user.o \ signal.o sys.o kmod.o workqueue.o pid.o \ - rcupdate.o intermodule.o extable.o params.o posix-timers.o + rcupdate.o intermodule.o extable.o params.o posix-timers.o \ + kthread.o obj-$(CONFIG_FUTEX) += futex.o obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .32392-linux-2.6.0-test11-bk6/kernel/kthread.c .32392-linux-2.6.0-test11-bk6.updated/kernel/kthread.c --- .32392-linux-2.6.0-test11-bk6/kernel/kthread.c 1970-01-01 10:00:00.000000000 +1000 +++ .32392-linux-2.6.0-test11-bk6.updated/kernel/kthread.c 2003-12-09 17:42:29.000000000 +1100 @@ -0,0 +1,228 @@ +/* Kernel thread helper functions. + * Copyright (C) 2003 IBM Corporation, Rusty Russell. + * + * Everything uses keventd, so that we get a clean environment even if + * we're invoked from userspace (think modprobe, hotplug cpu). + */ +#include +#include +#include +#include +#include + +/* This makes sure only one kthread is being talked to at once. */ +static DECLARE_MUTEX(kthread_control); + +/* This coordinates communication between the kthread and routine + * controlling it. Strictly unneccessary, but without it it's barrier + * hell. */ +static spinlock_t ktm_lock = SPIN_LOCK_UNLOCKED; + +/* All thread comms is command -> ack, so we keep it simple. */ +struct kt_message +{ + struct task_struct *from, *to; + void *info; +}; + +static struct kt_message ktm; + +static void ktm_send(struct task_struct *to, void *info) +{ + spin_lock(&ktm_lock); + ktm.to = to; + ktm.from = current; + ktm.info = info; + if (ktm.to) + wake_up_process(ktm.to); + spin_unlock(&ktm_lock); +} + +static struct kt_message ktm_receive(void) +{ + struct kt_message m; + + for (;;) { + spin_lock(&ktm_lock); + if (ktm.to == current) + break; + current->state = TASK_INTERRUPTIBLE; + spin_unlock(&ktm_lock); + schedule(); + } + m = ktm; + spin_unlock(&ktm_lock); + return m; +} + +struct kthread +{ + int (*initfn)(void *data); + int (*corefn)(void *data); + void *data; + char *name; +}; + +/* Check if we're being told to stop. */ +static int time_to_die(struct kt_message *m) +{ + int ret = 0; + + spin_lock(&ktm_lock); + if (ktm.to == current && ktm.info == NULL) { + *m = ktm; + ret = 1; + } + spin_unlock(&ktm_lock); + return ret; +} + +static int kthread(void *data) +{ + /* Copy data: it's on keventd_init's stack */ + struct kthread k = *(struct kthread *)data; + struct kt_message m; + int ret = 0; + sigset_t blocked; + + strcpy(current->comm, k.name); + + /* Block and flush all signals. */ + sigfillset(&blocked); + sigprocmask(SIG_BLOCK, &blocked, NULL); + flush_signals(current); + + /* Send to spawn_kthread, so it knows who we are. */ + ktm_send(ktm.info, current); + + /* Receive from kthread_start or kthread_destroy */ + m = ktm_receive(); + if (!m.info) + goto stop; + if (k.initfn && (ret = k.initfn(k.data)) < 0) + goto stop; + ktm_send(m.from, current); + + for (;;) { + if (time_to_die(&m)) + break; + + /* If it fails, just wait until kthread_destroy. */ + if (k.corefn && (ret = k.corefn(k.data)) < 0) + k.corefn = NULL; + + if (time_to_die(&m)) + break; + + schedule(); + } + + current->state = TASK_RUNNING; +stop: + ktm_send(m.from, ERR_PTR(ret)); + return ret; +} + +struct kthread_create +{ + struct task_struct *result; + struct kthread k; + struct completion done; +}; + +/* We are keventd(). We create a thread. */ +static void spawn_kthread(void *data) +{ + struct kthread_create *kc = data; + int ret; + + /* Set up message so they know who their parent is. */ + ktm_send(NULL, current); + + /* We want our own signal handler (we take no signals by default). */ + ret = kernel_thread(kthread, &kc->k, CLONE_FS | CLONE_FILES | SIGCHLD); + if (ret < 0) + kc->result = ERR_PTR(ret); + else { + /* They tell us who they are. */ + struct kt_message m = ktm_receive(); + kc->result = m.info; + } + complete(&kc->done); +} + +struct task_struct *kthread_create(int (*initfn)(void *data), + int (*corefn)(void *data), + void *data, + const char namefmt[], + ...) +{ + va_list args; + struct kthread_create kc; + DECLARE_WORK(work, spawn_kthread, &kc); + /* Or, as we like to say, 16. */ + char name[sizeof(((struct task_struct *)0)->comm)]; + + va_start(args, namefmt); + vsnprintf(name, sizeof(name), namefmt, args); + va_end(args); + + init_completion(&kc.done); + kc.k.initfn = initfn; + kc.k.corefn = corefn; + kc.k.data = data; + kc.k.name = name; + + down(&kthread_control); + /* If we're being called to start the first workqueue, we + * can't use keventd. */ + if (!keventd_up()) + work.func(work.data); + else { + schedule_work(&work); + wait_for_completion(&kc.done); + } + up(&kthread_control); + return kc.result; +} + +static void wait_for_death(struct task_struct *k) +{ + while (!(k->state & TASK_ZOMBIE) && !(k->state & TASK_DEAD)) + yield(); +} + +struct task_struct *kthread_start(struct task_struct *k) +{ + struct kt_message m; + + get_task_struct(k); + + down(&kthread_control); + ktm_send(k, k); + m = ktm_receive(); + up(&kthread_control); + + if (IS_ERR(m.info)) + wait_for_death(k); + put_task_struct(k); + + return m.info; +} + +int kthread_destroy(struct task_struct *k) +{ + struct kt_message m; + + get_task_struct(k); + + down(&kthread_control); + ktm_send(k, NULL); + m = ktm_receive(); + up(&kthread_control); + + wait_for_death(k); + put_task_struct(k); + + return PTR_ERR(m.info); +} diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .32392-linux-2.6.0-test11-bk6/kernel/workqueue.c .32392-linux-2.6.0-test11-bk6.updated/kernel/workqueue.c --- .32392-linux-2.6.0-test11-bk6/kernel/workqueue.c 2003-09-22 10:27:38.000000000 +1000 +++ .32392-linux-2.6.0-test11-bk6.updated/kernel/workqueue.c 2003-12-09 17:42:29.000000000 +1100 @@ -359,6 +359,11 @@ void flush_scheduled_work(void) flush_workqueue(keventd_wq); } +int keventd_up(void) +{ + return keventd_wq != NULL; +} + int current_is_keventd(void) { struct cpu_workqueue_struct *cwq;