Re: [PATCH 1/5] mm/vmalloc.c: correct a few logic error for __insert_vmap_area()

From: David Rientjes
Date: Wed Sep 21 2016 - 18:45:28 EST

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.