From: Jan Beulich <jbeulich@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
George Dunlap <george.dunlap@citrix.com>,
Ian Jackson <iwj@xenproject.org>
Subject: Re: [PATCH 2/2][4.15?] x86: fix build when NR_CPUS == 1
Date: Tue, 2 Mar 2021 12:18:45 +0100 [thread overview]
Message-ID: <638c8ff4-d853-69b1-a6a0-1778b342ac8f@suse.com> (raw)
In-Reply-To: <YD4aKmAaYZ5xdTzP@Air-de-Roger>
On 02.03.2021 11:57, Roger Pau Monné wrote:
> On Tue, Mar 02, 2021 at 10:59:37AM +0100, Jan Beulich wrote:
>> On 01.03.2021 19:00, Roger Pau Monné wrote:
>>> On Mon, Mar 01, 2021 at 04:14:26PM +0100, Jan Beulich wrote:
>>>> On 01.03.2021 15:01, Roger Pau Monné wrote:
>>>>> On Mon, Mar 01, 2021 at 09:31:07AM +0100, Jan Beulich wrote:
>>>>>> In this case the compiler is recognizing that no valid array indexes
>>>>>> remain (in x2apic_cluster()'s access to per_cpu(cpu_2_logical_apicid,
>>>>>> ...)), but oddly enough isn't really consistent about the checking it
>>>>>> does (see the code comment).
>>>>>
>>>>> I assume this is because of the underlying per_cpu access to
>>>>> __per_cpu_offset using cpu as the index, in which case wouldn't it be
>>>>> better to place the BUG_ON there?
>>>>
>>>> Not sure, to be honest. It seemed more logical to me to place it
>>>> next to where the issue is.
>>>
>>> I'm not sure whether I would prefer to place it in per_cpu directly to
>>> avoid similar issues popping up in other parts of the code in the
>>> future?
>>
>> That's going to be a lot of BUG_ON(), and hence a lot of "ud2"
>> instances. Not something I'm keen on having. The more that it's
>> not the per_cpu() which triggers the warning, but separate
>> conditionals allowing the compiler to deduce value ranges of
>> variables.
>
> Right. I don't see much other way around this then. Did you check with
> clang also?
No, I didn't. But if anything it would require further additions,
surely no less.
> Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Thanks.
Jan
next prev parent reply other threads:[~2021-03-02 11:18 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-01 8:27 [PATCH 0/2][4.15?] fix build when NR_CPUS == 1 Jan Beulich
2021-03-01 8:30 ` [PATCH 1/2][4.15?] sched: " Jan Beulich
2021-03-01 15:57 ` Ian Jackson
2021-03-01 17:50 ` Dario Faggioli
2021-03-01 8:31 ` [PATCH 2/2][4.15?] x86: " Jan Beulich
2021-03-01 14:01 ` Roger Pau Monné
2021-03-01 15:14 ` Jan Beulich
2021-03-01 18:00 ` Roger Pau Monné
2021-03-02 9:59 ` Jan Beulich
2021-03-02 10:57 ` Roger Pau Monné
2021-03-02 11:18 ` Jan Beulich [this message]
2021-03-01 16:03 ` Ian Jackson
2021-03-02 10:02 ` Jan Beulich
2021-03-02 12:28 ` Ian Jackson
2021-03-02 13:37 ` Jan Beulich
2021-03-01 8:33 ` [PATCH 0/2][4.15?] " Jan Beulich
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