linux-kernel - Re: [PATCH] module loader should not complain about unknown symbol

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Message-Id: <200711130923.12616.rusty@rustcorp.com.au>
Date:	Tue, 13 Nov 2007 09:23:12 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jan Glauber <jang@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Andi Kleen <andi@...stfloor.org>,
	Jon Masters <jonathan@...masters.org>
Subject: Re: [PATCH] module loader should not complain about unknown symbol

On Tuesday 13 November 2007 01:18:27 Jan Glauber wrote:
> If module A depends on module B and module B has not yet finished its
> init() the module loader may print a warning about an unknown symbol.
>
> This happens if module B is still in state MODULE_STATE_COMING,
> as module A runs into resolve_symbol() for a symbol from module B.
> resolve_symbol() return 0 in that case and causes the warning.

It also happens when a symbol is undefined, so this patch is a bad idea.

To do this properly you would change strong_try_module_get to return -EBUSY 
and -ENOENT, then change use_module(), then finally resolve_symbol(), then 
only print a warning when it returns something other than -EBUSY.

Better might be to put in a waitqueue and wake it up whenever a module is 
deleted or changes status.  Then use_module() can wait if 
strong_try_module_get() returns -EBUSY (up to 30 seconds, then print a 
warning and fail).

Hope that helps,
Rusty.
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