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

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Date:   Wed, 21 Sep 2016 14:10:49 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     zijun_hu <zijun_hu@...o.com>
cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, zijun_hu@....com, 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 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.