From: Linus Torvalds <torvalds@linux-foundation.org>
To: Eric Dumazet <edumazet@google.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
syzbot <syzbot+3ef049d50587836c0606@syzkaller.appspotmail.com>,
Marco Elver <elver@google.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>
Subject: Re: KCSAN: data-race in __alloc_file / __alloc_file
Date: Fri, 8 Nov 2019 12:30:35 -0800 [thread overview]
Message-ID: <CAHk-=wi-aTQx5-gD51QC6UWJYxQv1p1CnrPpfbn4X1S4AC7G-g@mail.gmail.com> (raw)
In-Reply-To: <CANn89i+RrngUr11_iOYDuqDvAZnPfG3ieJR025M78uhiwEPuvQ@mail.gmail.com>
On Fri, Nov 8, 2019 at 9:56 AM Eric Dumazet <edumazet@google.com> wrote:
>
> BTW, I would love an efficient ADD_ONCE(variable, value)
>
> Using WRITE_ONCE(variable, variable + value) is not good, since it can
> not use the optimized instructions operating directly on memory.
So I'm having a hard time seeing how this could possibly ever be valid.
Is this a "writer is locked, readers are unlocked" case or something?
Because we don't really have any sane way to do that any more
efficiently, unless we'd have to add new architecture-specific
functions for it (like we do have fo the percpu ops).
Anyway, if you have a really hot case you care about, maybe you could
convince the gcc people to just add it as a peephole optimization?
Right now, gcc ends up doing some strange things with volatiles, and
basically disables a lot of stuff over them. But with a test-case,
maybe you can convince somebody that certain optimizations are still
fine. A "read+add+write" really does the exact same accesses as an
add-to-memory instruction, but gcc has some logic to disable that
instruction fusion.
Linus
next prev parent reply other threads:[~2019-11-08 20:30 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 13:16 KCSAN: data-race in __alloc_file / __alloc_file 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 [this message]
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
[not found] <CAHk-=wjB61GNmqpX0BLA5tpL4tsjWV7akaTc2Roth7uGgax+mw@mail.gmail.com>
2019-11-10 16:09 ` 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
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
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