Messages in this thread Patch in this message | | | Date | Tue, 22 Jul 2008 17:59:38 +0900 | From | Akinobu Mita <> | Subject | Re: + workqueue-proper-error-unwinding-in-cpu-hotplug-error-path.patch added to -mm tree |
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On Tue, Jul 22, 2008 at 12:45:26PM +0400, Oleg Nesterov wrote: > On 07/22, Andrew Morton wrote: > > > > From: Akinobu Mita <akinobu.mita@gmail.com> > > > > Add proper error unwinding in error path in CPU_UP_PREPARE notifier. > > Could you clarify?
Sure.
> > --- a/kernel/workqueue.c~workqueue-proper-error-unwinding-in-cpu-hotplug-error-path > > +++ a/kernel/workqueue.c > > @@ -928,6 +928,15 @@ static int __devinit workqueue_cpu_callb > > break; > > printk(KERN_ERR "workqueue [%s] for %i failed\n", > > wq->name, cpu); > > + > > + list_for_each_entry_continue_reverse(wq, &workqueues, > > + list) { > > + cwq = per_cpu_ptr(wq->cpu_wq, cpu); > > + start_workqueue_thread(cwq, -1); > > + cleanup_workqueue_thread(cwq); > > + } > > + cpu_clear(cpu, cpu_populated_map); > > + > > return NOTIFY_BAD; > > If CPU_UP_PREPARE fails, _cpu_up() sends CPU_UP_CANCELED, and afaics > workqueue_cpu_callback() correctly cleanups cwq->thread's.
_cpu_up() does not send CPU_UP_CANCELED to the callback which has returned NOTIFY_BAD.
The behavior was changed by this commit:
commit a0d8cdb652d35af9319a9e0fb7134de2a276c636 Author: Akinobu Mita <akinobu.mita@gmail.com> Date: Thu Oct 18 03:05:12 2007 -0700
cpu hotplug: cpu: deliver CPU_UP_CANCELED only to NOTIFY_OKed callbacks with CPU_UP_PREPARE
The functions in a CPU notifier chain is called with CPU_UP_PREPARE event before making the CPU online. If one of the callback returns NOTIFY_BAD, it stops to deliver CPU_UP_PREPARE event, and CPU online operation is canceled. Then CPU_UP_CANCELED event is delivered to the functions in a CPU notifier chain again.
This CPU_UP_CANCELED event is delivered to the functions which have been called with CPU_UP_PREPARE, not delivered to the functions which haven't been called with CPU_UP_PREPARE.
The problem that makes existing cpu hotplug error handlings complex is that the CPU_UP_CANCELED event is delivered to the function that has returned NOTIFY_BAD, too.
Usually we don't expect to call destructor function against the object that has failed to initialize. It is like:
err = register_something(); if (err) { unregister_something(); return err; } So it is natural to deliver CPU_UP_CANCELED event only to the functions that have returned NOTIFY_OK with CPU_UP_PREPARE event and not to call the function that have returned NOTIFY_BAD. This is what this patch is doing. Otherwise, every cpu hotplug notifiler has to track whether notifiler event is failed or not for each cpu. (drivers/base/topology.c is doing this with topology_dev_map) Similary this patch makes same thing with CPU_DOWN_PREPARE and CPU_DOWN_FAILED evnets. Acked-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/cpu.c b/kernel/cpu.c index 38033db..a21f71a 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -150,6 +150,7 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen) err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls); if (err == NOTIFY_BAD) { + nr_calls--; __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL); printk("%s: attempt to take down CPU %u failed\n", @@ -233,6 +234,7 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls); if (ret == NOTIFY_BAD) { + nr_calls--; printk("%s: attempt to bring up CPU %u failed\n", __FUNCTION__, cpu); ret = -EINVAL;
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