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

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Date:   Mon, 3 May 2021 16:08:47 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Michel Lespinasse <michel@...pinasse.org>
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()

* Michel Lespinasse <michel@...pinasse.org> [210501 01:04]:
> 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.

Okay, I will make that change.

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

Thanks,
Liam