linux-kernel - running get_user_pages() from kernel thread

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Message-ID: <4A37DEE7.1000208@redhat.com>
Date:	Tue, 16 Jun 2009 21:05:27 +0300
From:	Izik Eidus <ieidus@...hat.com>
To:	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>
CC:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrea Arcangeli <aarcange@...hat.com>, nickpiggin@...oo.com.au
Subject: running get_user_pages() from kernel thread

Hey,

ksm is running from its kernel thread context get_user_pages(), but look 
like it isnt safe to do get_user_pages() from kernel thread:
get_user_pages may lead into do_swap_page() that may lead into calling 
grab_swap_token()

Now grab_swap_token() will do:
current_interval = global_faults - current->mm->... (here is the bug... 
(kernel thread doesnt have mm strcture)

So the question is: is this thing is by desgin? (that kernel thread cant 
call get_user_pages???), should i use something like switch_mm()??

Thanks.


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