From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
linux-next <linux-next@vger.kernel.org>,
KVM list <kvm@vger.kernel.org>
Subject: Re: [GIT PULL] locking fixes
Date: Mon, 23 Feb 2015 09:35:34 +0100 [thread overview]
Message-ID: <54EAE656.9000504@de.ibm.com> (raw)
In-Reply-To: <CA+55aFwT8TCfOh25FH-MP8FB2EBg-gexmU9Cn9beBAx+TQ1N4Q@mail.gmail.com>
Am 21.02.2015 um 02:51 schrieb Linus Torvalds:
> So here's my try at fixing READ_ONCE() so that it is happy with 'const' sources.
>
> It is entirely untested. Comments/testing?
>
> Christian, I guess I could just have forced a cast instead of the
> union. I'd like you to take a look at this, because right now it's
> holding up me pulling from Ingo.
Sorry for the too late for rc1 answer, but I was traveling the last 4
days.
Hmm, some autocasting feels better, but I could not come up with a proper
solution that works for all cases (e.g. I tried "__auto_type __val = x"
or "typeof(x * 0)" to make this lvalue and rvalue, but all variants failed
in one or the other way).
Unless I can come up with a better solution your union patch is probably
the best way to go and rc1 seems to work.
>
> And Ingo, I think you need to add some kind of test for "horrible new
> warnings". I think your pull request *worked*, but the tens of lines
> of new warnings it generates is unacceptable, and will just cause me
> to undo the pull if I notice in time (like I did this time).
I was getting several complaints from the linux-next buildbots about new
sparse warnings, compile warning and so on when doing this rework, e.g.
commit c5b19946eb76c675 ("kernel: Fix sparse warning for ACCESS_ONCE")
fixes two of those warnings.
So I am somewhat surprised that I never saw this as I am also following the
KVM list. turns out that arch/x86/kernel/kvm.c does not CC the kvm list
in get_maintainers.pl.
Maybe I should push something like that to Paolo/Marcelo.
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5574,6 +5574,7 @@ S: Supported
F: Documentation/*/kvm*.txt
F: Documentation/virtual/kvm/
F: arch/*/kvm/
+F: arch/x86/kernel/kvm.c
F: arch/*/include/asm/kvm*
F: include/linux/kvm*
F: include/uapi/linux/kvm*
Christian
>
> Linus
>
> On Fri, Feb 20, 2015 at 4:03 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> How does this work for you at all?
>>
>> On Fri, Feb 20, 2015 at 5:37 AM, Ingo Molnar <mingo@kernel.org> wrote:
>>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>>> index 94f643484300..e354cc6446ab 100644
>>> --- a/arch/x86/kernel/kvm.c
>>> +++ b/arch/x86/kernel/kvm.c
>>> @@ -803,8 +808,8 @@ static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
>>> add_stats(RELEASED_SLOW, 1);
>>> for_each_cpu(cpu, &waiting_cpus) {
>>> const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
>>> - if (ACCESS_ONCE(w->lock) == lock &&
>>> - ACCESS_ONCE(w->want) == ticket) {
>>> + if (READ_ONCE(w->lock) == lock &&
>>> + READ_ONCE(w->want) == ticket) {
>>> add_stats(RELEASED_SLOW_KICKED, 1);
>>> kvm_kick_cpu(cpu);
>>> break;
>>
>> I get horrible compile warnings from this, because of how 'w' is a
>> pointer to a 'const' structure, which then causes things like
>>
>> include/linux/compiler.h:262:39: warning: passing argument 1 of
>> ‘__read_once_size’ discards ‘const’ qualifier from pointer target type
>> ({ typeof(x) __val; __read_once_size(&x, &__val, sizeof(__val)); __val; })
>>
>> which is fairly hard to avoid (looks like it might need a union)
>>
>> Linus
next prev parent reply other threads:[~2015-02-23 8:35 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-20 13:37 [GIT PULL] locking fixes Ingo Molnar
2015-02-21 0:03 ` Linus Torvalds
2015-02-21 1:51 ` Linus Torvalds
2015-02-23 8:35 ` Christian Borntraeger [this message]
2015-02-21 5:07 ` Ingo Molnar
2015-02-21 5:16 ` Ingo Molnar
2015-02-21 5:28 ` Ingo Molnar
-- strict thread matches above, loose matches on Subject: below --
2023-09-22 10:12 Ingo Molnar
2023-09-22 20:19 ` pr-tracker-bot
2021-07-11 13:22 Ingo Molnar
2021-07-11 18:22 ` pr-tracker-bot
2021-04-11 12:14 Ingo Molnar
2021-04-11 18:56 ` pr-tracker-bot
2021-03-21 10:53 Ingo Molnar
2021-03-21 18:45 ` pr-tracker-bot
2020-12-27 9:50 Ingo Molnar
2020-12-27 17:27 ` pr-tracker-bot
2020-08-15 11:13 Ingo Molnar
2020-08-16 1:55 ` pr-tracker-bot
2020-01-18 17:53 Ingo Molnar
2020-01-18 21:05 ` pr-tracker-bot
2019-12-17 11:27 Ingo Molnar
2019-12-17 19:20 ` pr-tracker-bot
2019-04-20 7:30 Ingo Molnar
2019-04-20 16:51 ` Linus Torvalds
2019-04-21 18:23 ` Ingo Molnar
2019-04-20 19:25 ` pr-tracker-bot
2019-02-10 8:53 Ingo Molnar
2019-02-10 18:30 ` pr-tracker-bot
2018-10-05 9:36 Ingo Molnar
2018-10-05 23:06 ` Greg Kroah-Hartman
2018-09-15 12:56 Ingo Molnar
2018-07-30 17:49 Ingo Molnar
2018-03-25 8:49 Ingo Molnar
2018-02-15 0:50 Ingo Molnar
2018-01-17 15:24 Ingo Molnar
2018-01-22 9:43 ` Geert Uytterhoeven
2018-01-22 10:39 ` Peter Zijlstra
2018-01-12 13:45 Ingo Molnar
2017-12-15 15:55 Ingo Molnar
2017-10-14 16:01 Ingo Molnar
2017-03-07 20:27 Ingo Molnar
2017-02-28 7:57 Ingo Molnar
2017-02-28 18:37 ` Linus Torvalds
2017-05-03 23:21 ` Linus Torvalds
2017-05-04 5:40 ` Peter Zijlstra
[not found] ` <CA+55aFymvtCAYHdz__3Lj=YqmORB7_A-NXrw=+h+60znJVsDTw@mail.gmail.com>
2017-05-04 22:44 ` Greg Kroah-Hartman
2016-12-07 18:42 Ingo Molnar
2016-10-18 10:55 Ingo Molnar
2016-08-18 20:34 Ingo Molnar
2016-08-12 19:32 Ingo Molnar
2016-06-10 12:45 Ingo Molnar
2016-04-28 17:52 Ingo Molnar
2016-04-23 11:22 Ingo Molnar
2016-03-24 7:47 Ingo Molnar
2015-09-17 7:57 Ingo Molnar
2015-04-18 15:15 Ingo Molnar
2015-01-11 8:39 Ingo Molnar
2014-10-31 11:06 Ingo Molnar
2014-04-16 11:39 Ingo Molnar
2014-01-15 18:15 Ingo Molnar
2009-12-10 19:45 Ingo Molnar
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