linux-kernel - Re: [PATCH 3/4] mmap locking API: Don't check locking if the mm isn't live yet

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Message-ID: <20200930123000.GC9916@ziepe.ca>
Date:   Wed, 30 Sep 2020 09:30:00 -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 3/4] mmap locking API: Don't check locking if the mm
 isn't live yet

On Tue, Sep 29, 2020 at 06:20:00PM -0700, Jann Horn wrote:
> In preparation for adding a mmap_assert_locked() check in
> __get_user_pages(), teach the mmap_assert_*locked() helpers that it's fine
> to operate on an mm without locking in the middle of execve() as long as
> it hasn't been installed on a process yet.

I'm happy to see lockdep being added here, but can you elaborate on
why add this mmap_locked_required instead of obtaining the lock in the
execv path?

Jason