Messages in this thread | | | Date | Mon, 30 Jun 2008 15:43:49 +0200 | From | Heiko Carstens <> | Subject | Re: [PATCH 1/2] workqueues: make get_online_cpus() useable for work->func() |
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On Sun, Jun 29, 2008 at 08:51:31PM +0400, Oleg Nesterov wrote: > workqueue_cpu_callback(CPU_DEAD) flushes cwq->thread under > cpu_maps_update_begin(). This means that the multithreaded workqueues can't > use get_online_cpus() due to the possible deadlock, very bad and very old > problem. > > Introduce the new state, CPU_POST_DEAD, which is called after > cpu_hotplug_done() but before cpu_maps_update_done(). > > Change workqueue_cpu_callback() to use CPU_POST_DEAD instead of CPU_DEAD. > This means that create/destroy functions can't rely on get_online_cpus() > any longer and should take cpu_add_remove_lock instead.
Ah, nice!
> --- 26-rc2/kernel/cpu.c~WQ_4_GET_ONLINE_CPUS 2008-05-18 15:44:18.000000000 +0400 > +++ 26-rc2/kernel/cpu.c 2008-06-29 20:03:19.000000000 +0400 > @@ -261,6 +261,11 @@ out_allowed: > set_cpus_allowed_ptr(current, &old_allowed); > out_release: > cpu_hotplug_done(); > + if (!err) {
This should be (!err && !cpu_online(cpu)), no?
This is because it might be that __stop_machine_run() succeeded, but take_cpu_down() failed and therefore our cpu is still online.
Which in turn is not good when doing this:
> + if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod, > + hcpu) == NOTIFY_BAD) > + BUG(); > + }
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