linux-kernel - Re: [PATCH] fix error handling in load

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Message-ID: <20090922101046.GA8316@linux.vnet.ibm.com>
Date:	Tue, 22 Sep 2009 15:40:46 +0530
From:	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Eric Dumazet <dada1@...mosbay.com>,
	Am?rico Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH] fix error handling in load_module()

* Rusty Russell <rusty@...tcorp.com.au> [2009-09-22 14:35:21]:

> On Tue, 22 Sep 2009 12:11:21 am Tejun Heo wrote:
> > Hello, Andrew.
> > 
> > Andrew Morton wrote:
> > > My reverse engineering of the secret, undocumented percpu_modfree()
> > > indicates that its mad inventor intended that percpu_modfree(NULL) be a
> > > valid thing to do.
> > > 
> > > It calls free_percpu(), all implementations of which appear to secretly
> > > support free_percpu(NULL).
> > 
> > Eh... unfortunately, the original percpu_modfree() implementation
> > didn't seem to support it.
> 
> OK, I'll Andrew's fix for Tejun, and after his (spot-on!) comment about
> percpu_modfree never taking NULL, I've fixed the one caller to match
> the other two:
> 
> Subject: module: don't call percpu_modfree on NULL pointer.
> 
> The general one handles NULL, the static obsolescent
> (CONFIG_HAVE_LEGACY_PER_CPU_AREA) one in module.c doesn't; Eric's
> commit 720eba31 assumed it did, and various frobbings since then kept
> that assumption.
> 
> All other callers in module.c all protect it with an if; this effectively
> does the same as free_init is only goto if we fail percpu_modalloc().

Thanks, the patch fixes the issue.

> Reported-by: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Eric Dumazet <dada1@...mosbay.com>
> Cc: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Américo Wang <xiyou.wangcong@...il.com>
> 
> diff --git a/kernel/module.c b/kernel/module.c
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2522,8 +2522,8 @@ static noinline struct module *load_modu
>   free_unload:
>  	module_unload_free(mod);
>  #if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
> +	percpu_modfree(mod->refptr);
>   free_init:
> -	percpu_modfree(mod->refptr);
>  #endif
>  	module_free(mod, mod->module_init);
>   free_core:
> --
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			Kamalesh
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