linux-kernel - Re: fs/jffs2/readinode.c:189: faulty logic ?

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Message-ID: <87d819b7-8267-7d43-67b0-56c437c9290e@gmail.com>
Date:   Tue, 24 Jan 2017 16:14:02 +0100
From:   Marek Vasut <marek.vasut@...il.com>
To:     Joakim Tjernlund <Joakim.Tjernlund@...inera.com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "dcb314@...mail.com" <dcb314@...mail.com>
Subject: Re: fs/jffs2/readinode.c:189: faulty logic ?

On 01/24/2017 04:11 PM, Joakim Tjernlund wrote:
> On Tue, 2017-01-24 at 15:52 +0100, Marek Vasut wrote:
>> On 01/24/2017 09:15 AM, David Binderman wrote:
>>> Hello there,
>>>
>>> fs/jffs2/readinode.c:189]: (style) Condition 'tn.fn.ofs>=offset' is always true
>>>
>>> Source code is
>>>
>>>         if (tn->fn->ofs < offset)
>>>             next = tn->rb.rb_right;
>>>         else if (tn->fn->ofs >= offset)
>>>             next = tn->rb.rb_left;
>>>         else
>>>             break;
>>>
>>> Maybe better code
>>>
>>>         if (tn->fn->ofs < offset)
>>>             next = tn->rb.rb_right;
>>>         else if (tn->fn->ofs > offset)
>>>             next = tn->rb.rb_left;
>>>         else
>>>             break;
>>
>> This changes the logic of the code for equality case, please elaborate
>> why this is OK.
> 
> There is something odd with current code:
> 	next = tn_root->rb_node;
> 
> 	while (next) {
> 		tn = rb_entry(next, struct jffs2_tmp_dnode_info, rb);
> 
> 		if (tn->fn->ofs < offset)
> 			next = tn->rb.rb_right;
> 		else if (tn->fn->ofs >= offset)
> 			next = tn->rb.rb_left;
> 		else
> 			break;
> 	}
> 
> The else break; is never reached so the above change makes the break work for ==
> Weather this is correct or not I cannot say.

Indeed, I agree with this one. This is why I asked for more detailed
explanation too :)

-- 
Best regards,
Marek Vasut