linux-kernel - Re: KCSAN: data-race in __alloc_file / __alloc

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Date:   Mon, 11 Nov 2019 12:43:45 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Marco Elver <elver@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        syzbot <syzbot+3ef049d50587836c0606@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrea Parri <parri.andrea@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@...il.com>
Subject: Re: KCSAN: data-race in __alloc_file / __alloc_file

On Mon, Nov 11, 2019 at 11:13 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> What about this other one, it looks like multiple threads can
> manipulate tsk->min_flt++; at the same time  in faultin_page()

Yeah, maybe we could have some model for marking "this is statistics,
doesn't need to be exact".

> Should we not care, or should we mirror min_flt with a second
> atomic_long_t, or simply convert min_flt to atomic_long_t ?

Definitely not make it atomic. Those are expensive, and there's no point.

                    Linus