linux-kernel - Re: [PATCH 1/5] mm/vmalloc.c: correct a few logic error for __insert_vmap

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Date:   Thu, 22 Sep 2016 06:35:19 +0800
From:   zijun_hu <zijun_hu@...o.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     zijun_hu@....com, Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, tj@...nel.org,
        mingo@...nel.org, iamjoonsoo.kim@....com,
        mgorman@...hsingularity.net
Subject: Re: [PATCH 1/5] mm/vmalloc.c: correct a few logic error for
 __insert_vmap_area()

On 2016/9/22 5:10, David Rientjes wrote:
> On Wed, 21 Sep 2016, zijun_hu wrote:
> 
>> From: zijun_hu <zijun_hu@....com>
>>
>> correct a few logic error for __insert_vmap_area() since the else
>> if condition is always true and meaningless
>>
>> in order to fix this issue, if vmap_area inserted is lower than one
>> on rbtree then walk around left branch; if higher then right branch
>> otherwise intersects with the other then BUG_ON() is triggered
>>
> 
> Under normal operation, you're right that the "else if" conditional should 
> always succeed: we don't want to BUG() unless there's a bug.  The original 
> code can catch instances when va->va_start == tmp_va->va_end where we 
> should BUG().  Your code silently ignores it.
> 
Hmm, the BUG_ON() appears in the original code, i don't introduce it.
it maybe be better to consider va->va_start == tmp_va->va_end as normal case
and should not BUG_ON() it since the available range of vmap_erea include
the start boundary but the end, BTW, represented as [start, end)

this patch correct the logic to that mentioned in the comments, it maybe be
more logical and more understandable