linux-kernel - Re: [PATCH 11/12] sched: use for_each

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Date:   Mon, 9 Jul 2018 18:06:45 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 11/12] sched: use for_each_if in topology.h

On Mon, Jul 9, 2018 at 6:03 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Jul 09, 2018 at 05:52:04PM +0200, Daniel Vetter wrote:
>> for_each_something(foo)
>>       if (foo->bla)
>>               call_bla(foo);
>>       else
>>               call_default(foo);
>>
>> Totally contrived, but this complains. Liberally sprinkling {} also shuts
>> up the compiler, but it's a bit confusing given that a plain for {;;} is
>> totally fine. And it's confusing since at first glance the compiler
>> complaining about nested if and ambigous else doesn't make sense since
>> clearly there's only 1 if there.
>
> Ah, so the pattern the compiler tries to warn about is:
>
>         if (foo)
>                 if (bar)
>                         /* stmts1 */
>                 else
>                         /* stmts2 *
>
> Because it might not be immediately obvious with which if the else goes.
> Which is fair enough I suppose.

Yup. I'll augment the commit message of patch 1 to include this as
example, and why it's confusing in context of a for_each_foo macro
containing an if().

> OK, ACK.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch