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

From: David Daney
Date: Fri Jun 14 2013 - 12:35:59 EST

On 06/13/2013 10:46 PM, Linus Torvalds wrote:
On Thu, Jun 13, 2013 at 6:07 PM, David Daney <ddaney.cavm@xxxxxxxxx> 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..


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?


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