linux-kernel - Re: [PATCH 1/4] mm/gup_benchmark: Take the mmap lock around GUP

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Date:   Wed, 30 Sep 2020 09:20:14 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jann Horn <jannh@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Michel Lespinasse <walken@...gle.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH 1/4] mm/gup_benchmark: Take the mmap lock around GUP

On Tue, Sep 29, 2020 at 06:19:59PM -0700, Jann Horn wrote:
> To be safe against concurrent changes to the VMA tree, we must take the
> mmap lock around GUP operations (excluding the GUP-fast family of
> operations, which will take the mmap lock by themselves if necessary).
> 
> This code is only for testing, and it's only reachable by root through
> debugfs, so this doesn't really have any impact; however, if we want to add
> lockdep asserts into the GUP path, we need to have clean locking here.
> 
> Signed-off-by: Jann Horn <jannh@...gle.com>
> ---

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason