Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable
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- To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxxxx>
- Subject: Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Wed, 20 Apr 2016 11:04:05 -0700
- Cc: Ingo Molnar <mingo@xxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Chris Zankel <chris@xxxxxxxxxx>, Max Filippov <jcmvbkbc@xxxxxxxxx>, x86@xxxxxxxxxx, linux-alpha@xxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, sparclinux@xxxxxxxxxxxxxxx, linux-xtensa@xxxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
- In-reply-to: <20160420134019.GX3448@twins.programming.kicks-ass.net>
- List-id: <linux-ia64.vger.kernel.org>
- References: <1460041951-22347-1-git-send-email-mhocko@kernel.org> <1460041951-22347-11-git-send-email-mhocko@kernel.org> <20160413090829.GB29579@gmail.com> <20160413091625.GF14351@dhcp22.suse.cz> <20160413091943.GA17858@gmail.com> <20160413102731.GA29896@gmail.com> <20160413124943.GH14351@dhcp22.suse.cz> <20160420134019.GX3448@twins.programming.kicks-ass.net>
- User-agent: K-9 Mail for Android
On April 20, 2016 6:40:19 AM PDT, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>On Wed, Apr 13, 2016 at 02:49:43PM +0200, Michal Hocko wrote:
>> On Wed 13-04-16 12:27:31, Ingo Molnar wrote:
>> >
>> > * Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>> >
>> > > I'm testing your patches today, if they are otherwise OK [...]
>> >
>> > got this build failure:
>> >
>> > ./arch/x86/include/asm/rwsem.h:106:2: error: ‘asm’ operand has
>impossible constraints
>>
>> Hmm, I have no idea why 64b didn't have problem with the asm but 32b
>> complains. Anyway, the following makes both happy. I have checked the
>> generated code for 64b and it hasn't changed after the patch. 32b
>also
>> seems to be generating a proper code. My gcc asm()-foo is rather weak
>so
>> I would feel better if somebody double checked after me.
>
>I completely blow at this gcc-asm constraints thing too :/
>
>In any case, Ingo will you look after the rest of these patches, or do
>you want me to pick up the remaining bits?
The reason it breaks is because the same register can't be an input-output register and a separate input. However, the input side of the input-output is probably undefined, and so gcc may not notice.
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