From: Eric Dumazet <edumazet@google.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Marco Elver <elver@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>,
"Paul E. McKenney" <paulmck@kernel.org>,
LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>
Subject: Re: KCSAN: data-race in __alloc_file / __alloc_file
Date: Tue, 12 Nov 2019 14:07:03 -0800 [thread overview]
Message-ID: <CANn89iKjWH86kChzPiVtCgVpt3GookwGk2x1YCTMeBSPpKU+Ww@mail.gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1911121639540.1567-100000@iolanthe.rowland.org>
On Tue, Nov 12, 2019 at 1:48 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Tue, 12 Nov 2019, Linus Torvalds wrote:
>
> > Honestly, my preferred model would have been to just add a comment,
> > and have the reporting tool know to then just ignore it. So something
> > like
> >
> > + // Benign data-race on min_flt
> > tsk->min_flt++;
> > perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
> >
> > for the case that Eric mentioned - the tool would trigger on
> > "data-race", and the rest of the comment could/should be for humans.
> > Without making the code uglier, but giving the potential for a nice
> > leghibl.e explanation instead of a completely illegible "let's
> > randomly use WRITE_ONCE() here" or something like that.
>
> Just to be perfectly clear, then:
>
> Your feeling is that we don't need to tell the compiler anything at all
> about these races, because if a compiler generates code that is
> non-robust against such things then you don't want to use it for the
> kernel.
>
I would prefer some kind of explicit marking, instead of a comment.
Even if we prefer having a sane compiler, having these clearly
annotated can help
code readability quite a lot.
/*
* To use when we are ok with minor races... bla bla bla
*/
static void inline add_relaxed(int *p, int x)
{
x += __atomic_load_n(p, __ATOMIC_RELAXED);
__atomic_store_n(p, x, __ATOMIC_RELAXED);
}
The actual implementation might depend on the compiler, and revert to something
without any constraint for old compilers : *p += x;
next prev parent reply other threads:[~2019-11-12 22:07 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAHk-=wjB61GNmqpX0BLA5tpL4tsjWV7akaTc2Roth7uGgax+mw@mail.gmail.com>
2019-11-10 16:09 ` KCSAN: data-race in __alloc_file / __alloc_file Alan Stern
2019-11-10 19:10 ` Marco Elver
2019-11-11 15:51 ` Alan Stern
2019-11-11 16:51 ` Linus Torvalds
2019-11-11 17:52 ` Eric Dumazet
2019-11-11 18:04 ` Linus Torvalds
2019-11-11 18:31 ` Eric Dumazet
2019-11-11 18:44 ` Eric Dumazet
2019-11-11 19:00 ` Linus Torvalds
2019-11-11 19:13 ` Eric Dumazet
2019-11-11 20:43 ` Linus Torvalds
2019-11-11 20:46 ` Linus Torvalds
2019-11-11 21:53 ` Eric Dumazet
2019-11-11 23:51 ` Linus Torvalds
2019-11-12 16:50 ` Kirill Smelkov
2019-11-12 17:23 ` Linus Torvalds
2019-11-12 17:36 ` Linus Torvalds
2019-11-17 18:56 ` Kirill Smelkov
2019-11-17 19:20 ` Linus Torvalds
2019-11-11 18:50 ` Linus Torvalds
2019-11-11 18:59 ` Marco Elver
2019-11-11 18:59 ` Eric Dumazet
2019-11-10 19:12 ` Linus Torvalds
2019-11-10 19:20 ` Linus Torvalds
2019-11-10 20:44 ` Paul E. McKenney
2019-11-10 21:10 ` Linus Torvalds
2019-11-10 21:31 ` Paul E. McKenney
2019-11-11 14:17 ` Marco Elver
2019-11-11 14:31 ` Paul E. McKenney
2019-11-11 15:10 ` Marco Elver
2019-11-13 0:25 ` Paul E. McKenney
2019-11-12 19:14 ` Alan Stern
2019-11-12 19:47 ` Linus Torvalds
2019-11-12 20:29 ` Alan Stern
2019-11-12 20:58 ` Linus Torvalds
2019-11-12 21:13 ` Linus Torvalds
2019-11-12 22:05 ` Marco Elver
2019-11-12 21:48 ` Alan Stern
2019-11-12 22:07 ` Eric Dumazet [this message]
2019-11-12 22:44 ` Alexei Starovoitov
2019-11-12 23:17 ` Eric Dumazet
2019-11-12 23:40 ` Linus Torvalds
2019-11-13 15:00 ` Marco Elver
2019-11-13 16:57 ` Linus Torvalds
2019-11-13 21:33 ` Marco Elver
2019-11-13 21:50 ` Alan Stern
2019-11-13 22:48 ` Marco Elver
2019-11-08 13:16 syzbot
2019-11-08 13:28 ` Eric Dumazet
2019-11-08 17:01 ` Linus Torvalds
2019-11-08 17:22 ` Eric Dumazet
2019-11-08 17:38 ` Linus Torvalds
2019-11-08 17:53 ` Eric Dumazet
2019-11-08 17:55 ` Eric Dumazet
2019-11-08 18:02 ` Eric Dumazet
2019-11-08 18:12 ` Linus Torvalds
2019-11-08 20:30 ` Linus Torvalds
2019-11-08 20:53 ` Eric Dumazet
2019-11-08 21:36 ` Linus Torvalds
2019-11-08 18:05 ` Linus Torvalds
2019-11-08 18:15 ` Marco Elver
2019-11-08 18:40 ` Linus Torvalds
2019-11-08 19:48 ` Marco Elver
2019-11-08 20:26 ` Linus Torvalds
2019-11-08 21:57 ` Alan Stern
2019-11-08 22:06 ` Linus Torvalds
2019-11-09 23:08 ` Alan Stern
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CANn89iKjWH86kChzPiVtCgVpt3GookwGk2x1YCTMeBSPpKU+Ww@mail.gmail.com \
--to=edumazet@google.com \
--cc=akiyks@gmail.com \
--cc=elver@google.com \
--cc=eric.dumazet@gmail.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=parri.andrea@gmail.com \
--cc=paulmck@kernel.org \
--cc=stern@rowland.harvard.edu \
--cc=syzbot+3ef049d50587836c0606@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).