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Date: Thu, 29 Sep 2011 14:31:29 -0700
From: Andrew Morton <akpm00@gmail.com>
To: Jiri Kosina <jkosina@suse.cz>
Cc: Rusty Russell <rusty@rustcorp.com.au>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] kmod: prevent kmod_loop_msg overflow in
 __request_module()
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On Thu, 29 Sep 2011 17:50:45 +0200 (CEST)
Jiri Kosina <jkosina@suse.cz> wrote:

> Due to post-decrement

(post-increment)

> in condition of kmod_loop_msg in __request_module(),
> the system log can be spammed by much more than 5 instances of the 'runaway
> loop' message if the number of events triggering it makes the kmod_loop_msg
> to overflow.
> 
> Fix that by making sure we never increment it past the threshold.
> 
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
> ---
>  kernel/kmod.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/kmod.c b/kernel/kmod.c
> index ddc7644..a4bea97 100644
> --- a/kernel/kmod.c
> +++ b/kernel/kmod.c
> @@ -114,10 +114,12 @@ int __request_module(bool wait, const char *fmt, ...)
>  	atomic_inc(&kmod_concurrent);
>  	if (atomic_read(&kmod_concurrent) > max_modprobes) {
>  		/* We may be blaming an innocent here, but unlikely */
> -		if (kmod_loop_msg++ < 5)
> +		if (kmod_loop_msg < 5) {
>  			printk(KERN_ERR
>  			       "request_module: runaway loop modprobe %s\n",
>  			       module_name);
> +			kmod_loop_msg++;
> +		}
>  		atomic_dec(&kmod_concurrent);
>  		return -ENOMEM;
>  	}

Well, it will take two billion passes through here to cause the
overflow.  I really hope you found this problem by inspection!