From: Linus Torvalds <torvalds@linux-foundation.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: 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>,
"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 12:58:55 -0800 [thread overview]
Message-ID: <CAHk-=wgnjMEvqHnu_iJcbr_kdFyBQLhYojwv5T7p9F+CHxA9pg@mail.gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1911121515400.1567-100000@iolanthe.rowland.org>
On Tue, Nov 12, 2019 at 12:29 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> I'm trying to solve a real problem: How to tell KCSAN and the compiler
> that we don't care about certain access patterns which result in
> hardware-level races, and how to guarantee that the object code will
> still work correctly when those races occur. Not telling the compiler
> anything is a head-in-the-sand approach that will be dangerous in the
> long run.
I don't actually know how KCSAN ends up reading the annotations, but
since it's apparently not using the 'volatile' as a marker.
[ Goes off and fetches the thing ]
Ugh, that's just nasty.
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.
Could the KCSAN code be taught to do something like that by simply not
instrumenting it? Or, as mentioned, just have the reporting logic
maybe have a list of those comments (easily generated with some
variation of "git grep -in data-race" or something) and logic to just
ignore any report that comes from a line below that kind of comment?
Because I do not see a pretty way to annotate random things like this
that actually makes the code more legible. The READ_ONCE/WRITE_ONCE
annotations have not imho improved the code quality.
Linus
next prev parent reply other threads:[~2019-11-12 20:59 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 [this message]
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
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
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