linux-kernel - Re: [PATCH v2] staging: erofs: keep corrupted fs from crashing kernel in erofs_namei()

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Date:   Fri, 15 Feb 2019 18:33:30 +0800
From:   Gao Xiang <gaoxiang25@...wei.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
CC:     Chao Yu <yuchao0@...wei.com>, <devel@...verdev.osuosl.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Chao Yu <chao@...nel.org>, <linux-erofs@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        <weidu.du@...wei.com>, Al Viro <viro@...IV.linux.org.uk>,
        Miao Xie <miaoxie@...wei.com>, Fang Wei <fangwei1@...wei.com>
Subject: Re: [PATCH v2] staging: erofs: keep corrupted fs from crashing kernel
 in erofs_namei()

Hi Dan,

On 2019/2/15 17:35, Dan Carpenter wrote:
> On Fri, Feb 15, 2019 at 05:32:33PM +0800, Chao Yu wrote:
>> On 2019/2/15 15:57, Dan Carpenter wrote:
>>> On Fri, Feb 15, 2019 at 03:02:25PM +0800, Chao Yu wrote:
>>>> On 2019/2/1 20:16, Gao Xiang wrote:
>>>>> +	/*
>>>>> +	 * on-disk error, let's only BUG_ON in the debugging mode.
>>>>> +	 * otherwise, it will return 1 to just skip the invalid name
>>>>> +	 * and go on (in consideration of the lookup performance).
>>>>> +	 */
>>>>> +	DBG_BUGON(qd->name > qd->end);
>>>>
>>>> qd->name == qd->end is not allowed as well?
>>>>
>>>> So will it be better to return directly here?
>>>>
>>>> 	if (unlikely(qd->name >= qd->end)) {
>>>> 		DBG_BUGON(1);
>>>> 		return 1;
>>>> 	}
>>>
>>> Please don't add likely/unlikely() annotations unless you have
>>> benchmarked it and it makes a difference.
>>
>> Well, it only occur for corrupted image, since the image is readonly, so it
>> is really rare.
> 
> The likely/unlikely() annotations make the code harder to read.  It's
> only worth it if it's is a speedup on a fast path.

Yes, I think abuse of using likely/unlikely() should be avoided (I agree that
some odd likely/unlikely() exists in the current code, that should be cleaned up).

However, likely/unlikely()s are also clearly highlight critical/corner paths).
I personally think it should be used in case-by-case basis rather than a unified
conclusion ("that makes the code harder to read").

Thanks,
Gao Xiang

> 
> regards,
> dan carpenter
> 
> _______________________________________________
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> devel@...uxdriverproject.org
> http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
> 

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