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

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Date:   Sun, 10 Nov 2019 13:10:39 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Marco Elver <elver@...gle.com>,
        Eric Dumazet <edumazet@...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>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@...il.com>
Subject: Re: KCSAN: data-race in __alloc_file / __alloc_file

On Sun, Nov 10, 2019 at 12:44 PM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> But will "one size fits all" be practical and useful?

Oh, I do agree that if KCSAN has some mode where it says "I'll ignore
repeated writes with the same value" (or whatever), it could/should
likely be behind some flag.

I don't think it should be a subsystem flag, though. More of a "I'm
willing to actually analyze and ignore false positives" flag. Because
I don't think it's so much about the code, as it is about the person
who looks at the results.

For example, we're already getting push-back from people on some of
the KCSAN-inspired patches. If we have people sending patches to add
READ_ONCE/WRITE_ONCE to random places to shut up KCSAN reports, I
don't think that's good.

But if we have people who _work_ on memory ordering issues etc, and
want to see a strict mode, knowing there are false positives and able
to handle them, that's a completely different thing..

No?

              Linus