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Message-Id: <200705140757.33746.rjw@sisk.pl>
Date: Mon, 14 May 2007 07:57:32 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Oleg Nesterov <oleg@...sign.ru>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
Alex Dubov <oakad@...oo.com>, Pierre Ossman <drzeus@...eus.cx>
Subject: Re: 2.6.22-rc1: Broken suspend on SMP with tifm
On Sunday, 13 May 2007 23:34, Oleg Nesterov wrote:
> On 05/13, Rafael J. Wysocki wrote:
> >
[--snip--]
>
> > @@ -819,20 +843,31 @@ static int __devinit workqueue_cpu_callb
> >
> > +
> > + case CPU_DEAD_FROZEN:
> > + if (wq->freezeable) {
> > + take_over_work(wq, cpu);
> > + thaw_process(cwq->thread);
>
> Suppose that PF_NOFREEZE task T does flush_workqueue(), and CPU 1 has pending
> works. T does flush_cpu_workqueue(0), CPU_DEAD_FROZEN moves works from CPU 1
> to CPU 0, T does flush_cpu_workqueue(1) and finds nothing.
I think I have solved this particular problem without any locking:
Define an atomic field in workqueue_struct (let's call it 'switch'), initially
equal to 0. Whenever work is taken from an offlined CPU, take_over_work()
increases 'switch' by 1. In turn, flush_workqueue() reads 'switch' before
looping over CPUs and saves its value in a local variable. On exit, it
compares the current value of 'switch' with the saved one and if they differ,
it repeats the loop over CPUs.
Updated patch follows.
Rafael
---
kernel/workqueue.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 55 insertions(+), 3 deletions(-)
Index: linux-2.6.22-rc1/kernel/workqueue.c
===================================================================
--- linux-2.6.22-rc1.orig/kernel/workqueue.c
+++ linux-2.6.22-rc1/kernel/workqueue.c
@@ -62,6 +62,9 @@ struct workqueue_struct {
const char *name;
int singlethread;
int freezeable; /* Freeze threads during suspend */
+ atomic_t work_sw; /* Used to indicate that some work has been
+ * moved from one CPU to another
+ */
};
/* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
@@ -381,10 +384,15 @@ void fastcall flush_workqueue(struct wor
{
const cpumask_t *cpu_map = wq_cpu_map(wq);
int cpu;
+ int val;
might_sleep();
+ start:
+ val = atomic_read(&wq->work_sw);
for_each_cpu_mask(cpu, *cpu_map)
flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
+ if (unlikely(val != atomic_read(&wq->work_sw)))
+ goto start;
}
EXPORT_SYMBOL_GPL(flush_workqueue);
@@ -710,6 +718,7 @@ struct workqueue_struct *__create_workqu
wq->name = name;
wq->singlethread = singlethread;
wq->freezeable = freezeable;
+ atomic_set(&wq->work_sw, 0);
INIT_LIST_HEAD(&wq->list);
if (singlethread) {
@@ -791,6 +800,40 @@ void destroy_workqueue(struct workqueue_
}
EXPORT_SYMBOL_GPL(destroy_workqueue);
+/**
+ * take_over_work - if the workqueue is freezable and CPUs are being taken down
+ * due to a hibernation/suspend, we need to take the work out of their worker
+ * threads, because they might need to use some devices to do the work and
+ * the devices are suspended at this point.
+ * @wq: target workqueue
+ * @cpu: CPU being offlined
+ */
+static void take_over_work(struct workqueue_struct *wq, unsigned int cpu)
+{
+ struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
+ struct list_head list;
+ struct work_struct *work;
+
+ spin_lock_irq(&cwq->lock);
+ list_replace_init(&cwq->worklist, &list);
+
+ if (!list_empty(&list)) {
+ /*
+ * Tell flush_workqueue() that it should repeat the loop over
+ * CPUs
+ */
+ atomic_inc(&wq->work_sw);
+ while (!list_empty(&list)) {
+ printk("Taking work for %s\n", wq->name);
+ work = list_entry(list.next, struct work_struct, entry);
+ list_del(&work->entry);
+ __queue_work(per_cpu_ptr(wq->cpu_wq,
+ smp_processor_id()), work);
+ }
+ }
+ spin_unlock_irq(&cwq->lock);
+}
+
static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
unsigned long action,
void *hcpu)
@@ -799,9 +842,7 @@ static int __devinit workqueue_cpu_callb
struct cpu_workqueue_struct *cwq;
struct workqueue_struct *wq;
- action &= ~CPU_TASKS_FROZEN;
-
- switch (action) {
+ switch (action & ~CPU_TASKS_FROZEN) {
case CPU_LOCK_ACQUIRE:
mutex_lock(&workqueue_mutex);
return NOTIFY_OK;
@@ -819,20 +860,31 @@ static int __devinit workqueue_cpu_callb
switch (action) {
case CPU_UP_PREPARE:
+ case CPU_UP_PREPARE_FROZEN:
if (!create_workqueue_thread(cwq, cpu))
break;
printk(KERN_ERR "workqueue for %i failed\n", cpu);
return NOTIFY_BAD;
case CPU_ONLINE:
+ case CPU_ONLINE_FROZEN:
start_workqueue_thread(cwq, cpu);
break;
case CPU_UP_CANCELED:
+ case CPU_UP_CANCELED_FROZEN:
start_workqueue_thread(cwq, -1);
case CPU_DEAD:
cleanup_workqueue_thread(cwq, cpu);
break;
+
+ case CPU_DEAD_FROZEN:
+ if (wq->freezeable) {
+ take_over_work(wq, cpu);
+ thaw_process(cwq->thread);
+ }
+ cleanup_workqueue_thread(cwq, cpu);
+ break;
}
}
-
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