linux-kernel - Re: [PATCH] Fix some kallsyms

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Message-ID: <45F97A27.4030002@grupopie.com>
Date:	Thu, 15 Mar 2007 16:53:59 +0000
From:	Paulo Marques <pmarques@...popie.com>
To:	Alexey Dobriyan <adobriyan@...ru>
CC:	akpm@...l.org, linux-kernel@...r.kernel.org, devel@...nvz.org,
	mingo@...e.hu, tglx@...utronix.de, viro@...iv.linux.org.uk,
	rusty@...tcorp.com.au
Subject: Re: [PATCH] Fix some kallsyms_lookup() vs rmmod races

Alexey Dobriyan wrote:
> [cc'ing folks whose proc files are affected]
> 
> kallsyms_lookup() can call module_address_lookup() which iterates over
> modules list without module_mutex taken. Comment at the top of
> module_address_lookup() says it's for oops resolution so races are
> irrelevant, but in some cases it's reachable from regular code:

So maybe we should just add a new parameter to "kallsyms_lookup" to 
inform it if it is safe to take a mutex or not.

Spreading module_mutex everywhere doesn't seem like the right interface 
for several reasons:

  - new users of "kallsyms_lookup" might not be aware that they should 
take module_mutex if it is safe

  - many times we will be taking module_mutex even when we are fetching 
a kernel symbol that shouldn't require the mutex at all

  - it just creates new dependencies (hint: this patch shouldn't even 
compile with current git since module_mutex is not declared in module.h, 
not to mention compile when CONFIG_MODULES not set)

IMHO we should not expose module_mutex outside of module.c. That is just 
wrong from an encapsulation point of view.

-- 
Paulo Marques - www.grupopie.com

"667: The neighbor of the beast."

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