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Date:   Wed, 30 Sep 2020 09:20:14 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Jann Horn <jannh@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Michel Lespinasse <walken@google.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>
Subject: Re: [PATCH 1/4] mm/gup_benchmark: Take the mmap lock around GUP
Message-ID: <20200930122014.GB9916@ziepe.ca>
References: <CAG48ez3SG6ngZLtasxJ6LABpOnqCz5-QHqb0B4k44TQ8F9n6+w@mail.gmail.com>
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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@google.com>
> ---

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

Jason