linux-kernel - Re: [PATCH 01/13] AppArmor: misc. base functions and defines

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Date:	Fri, 30 Jul 2010 13:53:36 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	John Johansen <john.johansen@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>, xiaosuo@...il.com,
	laijs@...fujitsu.com
Subject: Re: [PATCH 01/13] AppArmor: misc. base functions and defines

On Fri, Jul 30, 2010 at 1:01 PM, John Johansen
<john.johansen@...onical.com> wrote:
>>> +/**
>>> + * kvfree - free an allocation do by kvmalloc
>>> + * @buffer: buffer to free (MAYBE_NULL)
>>> + *
>>> + * Free a buffer allocated by kvmalloc
>>> + */
>>> +void kvfree(void *buffer)
>>> +{
>>> +       if (is_vmalloc_addr(buffer)) {
>>> +               /* Data is no longer valid so just use the allocated space
>>> +                * as the work_struct
>>> +                */
>>> +               struct work_struct *work = (struct work_struct *) buffer;
>>> +               INIT_WORK(work, do_vfree);
>>> +               schedule_work(work);
>>
>> I don't understand this part here. Is it needed for interrupt contexts
>> or does vfree() sleep somewhere? If it's for the former, I think we
>> can just add a comment saying that kvmalloc/kvfree is not safe from
>> interrupt context and remove the schedule_work() parts here.
>
> vfree can sleep, and skipping the schedule_work parts won't work for
> apparmor as many of these allocations are being freed via rcu callbacks
> as most of our object life cycles are dependent on cred refcounting.

Can someone point me to where vfree() actually sleeps? I'm unable to
find the exact spot.
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