linux-kernel - Re: freezer problems

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Message-ID: <20070223190334.GA23599@in.ibm.com>
Date:	Sat, 24 Feb 2007 00:33:34 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Aneesh Kumar <aneesh.kumar@...il.com>, oleg@...sign.ru,
	linux-kernel@...r.kernel.org
Subject: Re: freezer problems

On Fri, Feb 23, 2007 at 04:32:01PM +0530, Srivatsa Vaddagiri wrote:
> On Fri, Feb 23, 2007 at 04:17:23PM +0530, Srivatsa Vaddagiri wrote:
> > Ok that was my point of concern. For hotplug we would ideally like
> > everyone to be frozen. If we are not freezing some (like vfork parents),
> > (rather if we dont -wait- for them to get frozen) before offlining a
> > cpu, then it may expose some hotplug unsafe code in the caller of vfork
> > in kernel - hopefully that is not a issue practically speaking.
> 
> I notice that __call_usermodehelper() work function calls kernel_thread with
> CLONE_VFORK set. __call_usermodehelper() is usualled called in the
> context of a worker thread (kevent).

But I see __call_usermodehelper being called from the context of
khelper_wq which is a singlethreaded workqueue.

I thought we were not planning to freeze singlethreaded workqueue's for
hotplug, since we are not kthread_stopping them anywhere.

So this kthread_stop waiting for parent(khelper_wq) which is blocked on
wait_for_complete(child->vfork_done) shouldn't occur. No?

Thanks and Regards
gautham.

-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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