linux-kernel - Re: Bug in find_vma_prev

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Message-ID: <alpine.LSU.2.00.1001311955510.6227@sister.anvils>
Date:	Sun, 31 Jan 2010 20:03:16 +0000 (GMT)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Tony Perkins <da.perk@...il.com>
cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-mm@...ck.org
Subject: Re: Bug in find_vma_prev - mmap.c

On Sun, 31 Jan 2010, Tony Perkins wrote:
> 
> Say for instance, that addr is not in the list (but is greater than
> the last element).

Before, you appeared to be talking about a discrepancy with the first
vma; now you're talking about a discrepancy with the last vma?
Or a discrepancy when the first vma is the last vma?

> find_vma_prev will return the last node in the list, whereas find_vma
> will return NULL.

I'd expect find_vma_prev to return prev->vm_next, which would be NULL.

> 
> It seems that it is just inconsistent, in what it should return
> regarding the two.
> For instance, find_vma_prev will never return NULL, if there's at
> least one node within the tree, whereas find_vma would.
> find_extend_vma uses find_vma_prev and checks to see if it returns
> NULL and is less than the return address (which would always be the
> case).

Are we disagreeing about our readings of the code, or have you seen a
problem in practice?

I admit I've not tried running this, injecting addresses into find_vma_prev
and printk'ing the result; but I'm missing what leads you to say that
find_vma_prev will never return NULL.

Hugh
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