Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable

From	"H. Peter Anvin" <hpa@zytor.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable
Date	2016-04-20 20:10 +0200
Message-ID	<rq4JC-3Ai-49@gated-at.bofh.it> (permalink)
References	(3 earlier) <rnp7Q-7vE-5@gated-at.bofh.it> <rnphw-7zX-21@gated-at.bofh.it> <rnqdA-8e7-25@gated-at.bofh.it> <rnsyK-1lV-15@gated-at.bofh.it> <rq0FY-fr-19@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On April 20, 2016 6:40:19 AM PDT, Peter Zijlstra <peterz@infradead.org> 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@kernel.org> 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.
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.

Thread

Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Peter Zijlstra <peterz@infradead.org> - 2016-04-20 15:50 +0200
  Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable "H. Peter Anvin" <hpa@zytor.com> - 2016-04-20 20:10 +0200
    Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Borislav Petkov <bp@alien8.de> - 2016-04-20 22:50 +0200
      Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Michal Hocko <mhocko@kernel.org> - 2016-04-20 23:00 +0200
      Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable "H. Peter Anvin" <hpa@zytor.com> - 2016-04-20 23:10 +0200
        Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Borislav Petkov <bp@alien8.de> - 2016-04-20 23:40 +0200
          Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable "H. Peter Anvin" <hpa@zytor.com> - 2016-04-21 00:40 +0200
            Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Borislav Petkov <bp@alien8.de> - 2016-04-21 13:40 +0200
              Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Michal Hocko <mhocko@kernel.org> - 2016-04-21 15:10 +0200
                Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Borislav Petkov <bp@alien8.de> - 2016-04-21 15:30 +0200
            [PATCH] x86/locking/rwsem: Cleanup ____down_write() Borislav Petkov <bp@alien8.de> - 2016-04-27 14:10 +0200
              [tip:locking/rwsem] locking/rwsem, x86: Clean up ____down_write() tip-bot for Borislav Petkov <tipbot@zytor.com> - 2016-04-28 12:30 +0200
  Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Ingo Molnar <mingo@kernel.org> - 2016-04-22 09:00 +0200

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