From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754483AbZCREYZ (ORCPT ); Wed, 18 Mar 2009 00:24:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752538AbZCREWZ (ORCPT ); Wed, 18 Mar 2009 00:22:25 -0400 Received: from ozlabs.org ([203.10.76.45]:59289 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751708AbZCREWV (ORCPT ); Wed, 18 Mar 2009 00:22:21 -0400 To: linux-kernel@vger.kernel.org From: Rusty Russell Date: Wed, 18 Mar 2009 10:40:24 +1030 Subject: [PATCH 1/9] work_on_cpu(): rewrite it to create a kernel thread on demand Cc: Ingo Molnar Cc: Andrew Morton Message-Id: <20090318042219.29196DDF4E@ozlabs.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andrew Morton The various implemetnations and proposed implemetnations of work_on_cpu() are vulnerable to various deadlocks because they all used queues of some form. Unrelated pieces of kernel code thus gained dependencies wherein if one work_on_cpu() caller holds a lock which some other work_on_cpu() callback also takes, the kernel could rarely deadlock. Fix this by creating a short-lived kernel thread for each work_on_cpu() invokation. This is not terribly fast, but the only current caller of work_on_cpu() is pci_call_probe(). It would be nice to find some other way of doing the node-local allocations in the PCI probe code so that we can zap work_on_cpu() altogether. The code there is rather nasty. I can't think of anything simple at this time... Cc: Rusty Russell Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Rusty Russell --- kernel/workqueue.c | 36 +++++++++++++++++++----------------- 1 file changed, 19 insertions(+), 17 deletions(-) diff -puN kernel/workqueue.c~work_on_cpu-rewrite-it-to-create-a-kernel-thread-on-demand kernel/workqueue.c --- a/kernel/workqueue.c~work_on_cpu-rewrite-it-to-create-a-kernel-thread-on-demand +++ a/kernel/workqueue.c @@ -985,20 +985,20 @@ undo: } #ifdef CONFIG_SMP -static struct workqueue_struct *work_on_cpu_wq __read_mostly; struct work_for_cpu { - struct work_struct work; + struct completion completion; long (*fn)(void *); void *arg; long ret; }; -static void do_work_for_cpu(struct work_struct *w) +static int do_work_for_cpu(void *_wfc) { - struct work_for_cpu *wfc = container_of(w, struct work_for_cpu, work); - + struct work_for_cpu *wfc = _wfc; wfc->ret = wfc->fn(wfc->arg); + complete(&wfc->completion); + return 0; } /** @@ -1009,17 +1009,23 @@ static void do_work_for_cpu(struct work_ * * This will return the value @fn returns. * It is up to the caller to ensure that the cpu doesn't go offline. + * The caller must not hold any locks which would prevent @fn from completing. */ long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg) { - struct work_for_cpu wfc; - - INIT_WORK(&wfc.work, do_work_for_cpu); - wfc.fn = fn; - wfc.arg = arg; - queue_work_on(cpu, work_on_cpu_wq, &wfc.work); - flush_work(&wfc.work); - + struct task_struct *sub_thread; + struct work_for_cpu wfc = { + .completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion), + .fn = fn, + .arg = arg, + }; + + sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu"); + if (IS_ERR(sub_thread)) + return PTR_ERR(sub_thread); + kthread_bind(sub_thread, cpu); + wake_up_process(sub_thread); + wait_for_completion(&wfc.completion); return wfc.ret; } EXPORT_SYMBOL_GPL(work_on_cpu); @@ -1035,8 +1041,4 @@ void __init init_workqueues(void) hotcpu_notifier(workqueue_cpu_callback, 0); keventd_wq = create_workqueue("events"); BUG_ON(!keventd_wq); -#ifdef CONFIG_SMP - work_on_cpu_wq = create_workqueue("work_on_cpu"); - BUG_ON(!work_on_cpu_wq); -#endif }