linux-kernel - Re: [PATCH 01/94] mm: Add vma

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Message-ID: <20210501050441.GB5188@lespinasse.org>
Date:   Fri, 30 Apr 2021 22:04:41 -0700
From:   Michel Lespinasse <michel@...pinasse.org>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>
Subject: Re: [PATCH 01/94] mm: Add vma_lookup()

On Wed, Apr 28, 2021 at 03:35:43PM +0000, Liam Howlett wrote:
> Many places in the kernel use find_vma() to get a vma and then check the
> start address of the vma to ensure the next vma was not returned.
> 
> Other places use the find_vma_intersection() call with add, addr + 1 as
> the range; looking for just the vma at a specific address.
> 
> The third use of find_vma() is by developers who do not know that the
> function starts searching at the provided address upwards for the next
> vma.  This results in a bug that is often overlooked for a long time.
> 
> Adding the new vma_lookup() function will allow for cleaner code by
> removing the find_vma() calls which check limits, making
> find_vma_intersection() calls of a single address to be shorter, and
> potentially reduce the incorrect uses of find_vma().
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>

This seems like a good API to have, and I agree it's less error prone than
having every caller check the vma->vm_start address.

Minor nitpick, I would prefer if the implementation used find_vma()
and then checked the vma->vm_start address - I don't like using [i, i+1)
intervals to implement stabbing queries.

But other than that, I think this (and the other patches adding
corresponding call sites) is safe for merging.

--
Michel "walken" Lespinasse