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Date:   Mon, 9 May 2022 10:07:03 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mm-commits@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
        luto@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com,
        bp@alien8.de, kunyu@nfschina.com
Subject: Re: + mm-functions-may-simplify-the-use-of-return-values.patch
 added to mm-unstable branch
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On Mon, 9 May 2022 09:20:35 +0200 Peter Zijlstra <peterz@infradead.org> wrote:

> 
> Please, no:
> 
> arch/x86/mm/pgtable.c: * p4d_clear_huge - clear kernel P4D mapping when it is set
> arch/x86/mm/pgtable.c:int p4d_clear_huge(p4d_t *p4d)
> arch/x86/mm/pgtable.c: * pud_clear_huge - clear kernel PUD mapping when it is set
> arch/x86/mm/pgtable.c:int pud_clear_huge(pud_t *pud)
> arch/x86/mm/pgtable.c: * pmd_clear_huge - clear kernel PMD mapping when it is set
> arch/x86/mm/pgtable.c:int pmd_clear_huge(pmd_t *pmd)
> 
> why would the p4d one need to be different from the rest?

Because the p4d one doesn't return anything, whereas the others do?

Any code which tests the p4d_clear_huge() return value is probably
buggy, so making p4d_clear_huge() return void permits us to detect such
a bug with the C type system.