linux-kernel - Re: [PATCH v2] sched/core: silence a warning in sched

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Date:   Tue, 25 Jun 2019 17:57:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Qian Cai <cai@....pw>
Cc:     mingo@...hat.com, valentin.schneider@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/core: silence a warning in sched_init()

On Tue, Jun 25, 2019 at 11:07:09AM -0400, Qian Cai wrote:
> On Tue, 2019-06-25 at 16:25 +0200, Peter Zijlstra wrote:
> > On Tue, Jun 25, 2019 at 10:04:19AM -0400, Qian Cai wrote:
> > > On Tue, 2019-06-25 at 15:52 +0200, Peter Zijlstra wrote:
> > > Yes, -Wmissing-prototype makes no sense, but "-Wunused-but-set-variable" is
> > > pretty valid to catch certain developer errors. For example,
> > > 
> > > https://lists.linuxfoundation.org/pipermail/iommu/2019-May/035680.html
> > > 
> > > > 
> > > > As to this one, ideally the compiler would not be stupid, and understand
> > > > the below, but alas.
> > > 
> > > Pretty sure that won't work, as the compiler will complain something like,
> > > 
> > > ISO C90 forbids mixed declarations and code
> > 
> > No, it builds just fine, it's a new block and C allows new variables at
> > every block start -- with the scope of that block.
> 
> I remember I tried that before but recalled the error code wrong. Here it is,
> 
> kernel/sched/core.c:5940:17: warning: unused variable 'ptr' [-Wunused-variable]
>                 unsigned long ptr = (unsigned long)kzalloc(alloc_size,
> GFP_NOWAIT);

Yes, I know, I tried. And GCC is a moron because of it.