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Message-Id: <200705132322.10032.rjw@sisk.pl>
Date: Sun, 13 May 2007 23:22:09 +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 22:50, Oleg Nesterov wrote:
> On 05/13, Rafael J. Wysocki wrote:
> >
> > On Sunday, 13 May 2007 22:30, Oleg Nesterov wrote:
> > > >
> > > > > --- linux-2.6.22-rc1.orig/kernel/workqueue.c
> > > > > +++ linux-2.6.22-rc1/kernel/workqueue.c
> > > > > @@ -799,9 +799,7 @@ 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) {
> > > >
> > > > Confused. How can we see, say CPU_UP_PREPARE_FROZEN, if we cleared
> > > > CPU_TASKS_FROZEN bit?
> > >
> > > So, unless I missed something stupid, this patch is not 100% right.
> >
> > Well, it isn't, but for a different reason (see [*] below).
>
> Yes, I missed something stupid :)
>
> > > I think the better fix (at least for now) is
> > >
> > > - #define create_freezeable_workqueue(name) __create_workqueue((name), 0, 1)
> > > + #define create_freezeable_workqueue(name) __create_workqueue((name), 1, 1)
> > >
> > > Alex, do you really need a multithreaded wq?
> > >
> > > Rafael, what do you think?
> >
> > That would be misleading if the driver needs the threads to be frozen.
>
> Hm? The thread will be frozen, the "patch" above changes "singlethread", not
> "freezeable".
Ah, I'm sorry.
> > [*] Getting back to the patch, it seems to me that we should do something like
> > take_over_work() before thawing the frozen thread, because there may be a queue
> > to process and the device is suspended at that point.
>
> Yes, exactly because the driver wants this wq to be frozen.
>
> So, could you take a second look at the "patch" above ?
Sure, if a singlethread workqueue is sufficient for Alex, I agree that this
would be preferable.
Anyway, I've added take_over_work() to the patch (appended), just in case. ;-)
Rafael
---
Prevent freezable worqueues from deadlocking with CPU hotplug during a
suspend/hibernation by thawing their worker threads before they get stopped.
Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
kernel/workqueue.c | 41 ++++++++++++++++++++++++++++++++++++++---
1 file changed, 38 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
@@ -791,6 +791,32 @@ 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);
+
+ 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 +825,7 @@ 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 +843,31 @@ 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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