Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <CAHk-=wjB61GNmqpX0BLA5tpL4tsjWV7akaTc2Roth7uGgax+mw@mail.gmail.com>
 <Pine.LNX.4.44L0.1911101034180.29192-100000@netrider.rowland.org>
 <CAHk-=wjErHCwkcgO-=NReU0KR4TFozrFktbhh2rzJ=mPgRO0-g@mail.gmail.com>
 <CAHk-=wghq7rmtskFj7EbngpXUTJfc4H9sDcx10E6kMHoH2EsKA@mail.gmail.com> <20191110204442.GA2865@paulmck-ThinkPad-P72>
In-Reply-To: <20191110204442.GA2865@paulmck-ThinkPad-P72>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 10 Nov 2019 13:10:39 -0800
Message-ID: <CAHk-=wjm40mcf7tk9DZQXd=dftZw_VpmE837c7pTZ1_cR+t4Mw@mail.gmail.com>
Subject: Re: KCSAN: data-race in __alloc_file / __alloc_file
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Alan Stern <stern@rowland.harvard.edu>,
        Marco Elver <elver@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        syzbot <syzbot+3ef049d50587836c0606@syzkaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andrea Parri <parri.andrea@gmail.com>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, Nov 10, 2019 at 12:44 PM Paul E. McKenney <paulmck@kernel.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