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

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Message-ID: <alpine.DEB.2.10.1609211544510.41473@chino.kir.corp.google.com>
Date:   Wed, 21 Sep 2016 15:45:19 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     zijun_hu <zijun_hu@...o.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 Thu, 22 Sep 2016, zijun_hu wrote:

> >> 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)
> 

We don't support inserting when va->va_start == tmp_va->va_end, plain and 
simple.  There's no reason to do so.  NACK to the patch.