linux-kernel - Re: [Bugme-new] [Bug 8957] New: Exported functions and variables should not be reachable by the outside of the module until module

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Message-Id: <20070829191043.91616ca7.akpm@linux-foundation.org>
Date:	Wed, 29 Aug 2007 19:10:43 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	bugme-daemon@...zilla.kernel.org, linux-kernel@...r.kernel.org,
	mattilinnanvuori@...oo.com
Subject: Re: [Bugme-new] [Bug 8957] New: Exported functions and variables
 should not be reachable by the outside of the module until module_init
 finishes

On Wed, 29 Aug 2007 19:33:48 -0600 Robert Hancock <hancockr@...w.ca> wrote:

> Andrew Morton wrote:
> > On Wed, 29 Aug 2007 11:33:06 -0700 (PDT) bugme-daemon@...zilla.kernel.org wrote:
> > 
> >> http://bugzilla.kernel.org/show_bug.cgi?id=8957
> >>
> >>            Summary: Exported functions and variables should not be reachable
> >>                     by the outside of the module until module_init finishes
> >>            Product: Other
> >>            Version: 2.5
> >>      KernelVersion: 2.6.23-rc4
> >>           Platform: All
> >>         OS/Version: Linux
> >>               Tree: Mainline
> >>             Status: NEW
> >>           Severity: normal
> >>           Priority: P1
> >>          Component: Modules
> >>         AssignedTo: other_modules@...nel-bugs.osdl.org
> >>         ReportedBy: mattilinnanvuori@...oo.com
> >>
> >>
> >> Problem Description: a module's exported functions can be called before before
> >> they are properly initialized by the module_init function.
> >>
> >> Steps to reproduce: write a module that exports functions that require
> >> initialization by the module_init function to work correctly.
> >>
> >> E.g. spin lock variables are no longer allowed to be initialized by C
> >> initializers of the module but only by spin_lock_init that can be called by the
> >> module_init function. If an exported function calls spin_lock before it is
> >> initialized, it deadlocks.
> >>
> > 
> > ooh, nice bug ;)
> 
> Under what circumstances is this actually happening? What are these 
> functions that are being called?
> 
> Normally things are set up such that this isn't a problem, i.e. if 
> module A depends on module B, module A can't load until module B is 
> finished loading.
> 

Good point.

This thus-far-undescribed module could make its internals externally
visible via one of the kernel's many register_foo() interfaces, but it
would be a buggy module if it was doing register_foo(my_foo) before
my_foo() was ready to be called.
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