linux-kernel - Re: [uml-devel] fuzz tested 32 bit user mode linux image hangs in radix_tree_next

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Date:	Sun, 10 Nov 2013 16:45:56 +0100
From:	Richard Weinberger <richard@....at>
To:	Toralf Förster <toralf.foerster@....de>
CC:	Konstantin Khlebnikov <koct9i@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	UML devel <user-mode-linux-devel@...ts.sourceforge.net>
Subject: Re: [uml-devel] fuzz tested 32 bit user mode linux image hangs in
 radix_tree_next_chunk()

Am 10.11.2013 16:14, schrieb Toralf Förster:
> On 11/06/2013 10:31 PM, Richard Weinberger wrote:
>> Am 06.11.2013 22:18, schrieb Toralf Förster:
>>> On 11/06/2013 05:06 PM, Konstantin Khlebnikov wrote:
>>>> In this case it must stop after scanning whole tree in line:
>>>> /* Overflow after ~0UL */
>>>> if (!index)
>>>>   return NULL;
>>>>
>>>
>>> A fresh current example with latest git tree shows that lines 769 and 770 do alternate :
>>
>> Can you please ask gdb for the value of offset?
>>
>> Thanks,
>> //richard
>>
> 
> With this change 
> 
> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index 7811ed3..b2e9db5 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -767,6 +767,7 @@ restart:
>                                                 offset + 1);
>                         else
>                                 while (++offset < RADIX_TREE_MAP_SIZE) {
> +                                       printk ("node->slots[offset] %p offeset %lu\n", node->slots[offset], offset);
>                                         if (node->slots[offset])
>                                                 break;
>                                 }

Make sure that you print only in case of a enless loop. i.e. add a loop counter
and start printing only if the loop was taken *very* often.

Thanks,
//richard
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