linux-mips
[Top] [All Lists]

Re: [PATCH] smp.h: Use local_irq_{save,restore}() in !SMP version of on_

To: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] smp.h: Use local_irq_{save,restore}() in !SMP version of on_each_cpu().
From: David Daney <ddaney@caviumnetworks.com>
Date: Fri, 14 Jun 2013 09:35:50 -0700
Cc: David Daney <ddaney.cavm@gmail.com>, Ralf Baechle <ralf@linux-mips.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mips <linux-mips@linux-mips.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, David Daney <david.daney@cavium.com>
In-reply-to: <CA+55aFziBGnSgLimDe7WBRPQ+f3RVAsrdbo212oj85c-XSz4oA@mail.gmail.com>
List-archive: <http://www.linux-mips.org/archives/linux-mips/>
List-help: <mailto:ecartis@linux-mips.org?Subject=help>
List-id: linux-mips <linux-mips.eddie.linux-mips.org>
List-owner: <mailto:ralf@linux-mips.org>
List-post: <mailto:linux-mips@linux-mips.org>
List-software: Ecartis version 1.0.0
List-subscribe: <mailto:ecartis@linux-mips.org?subject=subscribe%20linux-mips>
List-unsubscribe: <mailto:ecartis@linux-mips.org?subject=unsubscribe%20linux-mips>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1371172023-16004-1-git-send-email-ddaney.cavm@gmail.com> <CA+55aFziBGnSgLimDe7WBRPQ+f3RVAsrdbo212oj85c-XSz4oA@mail.gmail.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6
On 06/13/2013 10:46 PM, Linus Torvalds wrote:
On Thu, Jun 13, 2013 at 6:07 PM, David Daney <ddaney.cavm@gmail.com> wrote:

Suggested fix: Do what we already do in the SMP version of
on_each_cpu(), and use local_irq_save/local_irq_restore.

I was going to apply this, but started looking a bit more.

Using "flags" as a variable name inside a macro like this is a
*really* bad idea.

Lookie here:

     [torvalds@pixel linux]$ git grep on_each_cpu.*flags
     arch/s390/kernel/perf_cpum_cf.c:        on_each_cpu(setup_pmc_cpu,
&flags, 1);
     arch/s390/kernel/perf_cpum_cf.c:        on_each_cpu(setup_pmc_cpu,
&flags, 1);

and ask yourself what happens when the "info" argument expands to
"&flags", and it all compiles perfectly fine, but the "&flags" takes
the address of the new _inner_ variable called "flags" from the macro
expansion. Not the one that the caller actually intends..

Oops.

Not a good idea.


Yeah,  I think making it a static inline function may be the best approach.

I am going to test doing that and send a new patch very soon.

David Daney


So I would suggest trivially renaming "flags" as "__flags" or
something, or perhaps even just making it a real function and avoiding
the whole namespace issue.

And rather than doing that blindly by editing the patch at after -rc5,
I'm just going to ask you to re-send a tested patch. Ok?

                     Linus



<Prev in Thread] Current Thread [Next in Thread>