linux-kernel - Re: [PATCH v3 09/17] memblock: make memblock_debug and related functionality private

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Date:   Wed, 19 Aug 2020 12:24:05 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Baoquan He <bhe@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Hellwig <hch@....de>, Daniel Axtens <dja@...ens.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Emil Renner Berthing <kernel@...il.dk>,
        Ingo Molnar <mingo@...hat.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Simek <monstr@...str.eu>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Russell King <linux@...linux.org.uk>,
        Stafford Horne <shorne@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        clang-built-linux@...glegroups.com,
        iommu@...ts.linux-foundation.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-c6x-dev@...ux-c6x.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, linuxppc-dev@...ts.ozlabs.org,
        openrisc@...ts.librecores.org, sparclinux@...r.kernel.org,
        uclinux-h8-devel@...ts.sourceforge.jp, x86@...nel.org
Subject: Re: [PATCH v3 09/17] memblock: make memblock_debug and related
 functionality private

On Tue, 18 Aug 2020 18:16:26 +0300 Mike Rapoport <rppt@...nel.org> wrote:

> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> The only user of memblock_dbg() outside memblock was s390 setup code and it
> is converted to use pr_debug() instead.
> This allows to stop exposing memblock_debug and memblock_dbg() to the rest
> of the kernel.
> 
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -137,7 +137,10 @@ struct memblock_type physmem = {
>  	     i < memblock_type->cnt;					\
>  	     i++, rgn = &memblock_type->regions[i])
>  
> -int memblock_debug __initdata_memblock;
> +#define memblock_dbg(fmt, ...) \
> +	if (memblock_debug) printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
> +

checkpatch doesn't like this much.

ERROR: Macros starting with if should be enclosed by a do - while loop to avoid possible if/else logic defects
#101: FILE: mm/memblock.c:140:
+#define memblock_dbg(fmt, ...) \
+	if (memblock_debug) printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)

WARNING: Prefer [subsystem eg: netdev]_info([subsystem]dev, ... then dev_info(dev, ... then pr_info(...  to printk(KERN_INFO ...
#102: FILE: mm/memblock.c:141:
+	if (memblock_debug) printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)

ERROR: trailing statements should be on next line
#102: FILE: mm/memblock.c:141:
+	if (memblock_debug) printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)


The first one is significant:

	if (foo)
		memblock_dbg(...);
	else
		save_the_world();

could end up inadvertently destroying the planet.

This?

--- a/mm/memblock.c~memblock-make-memblock_debug-and-related-functionality-private-fix
+++ a/mm/memblock.c
@@ -137,8 +137,11 @@ struct memblock_type physmem = {
 	     i < memblock_type->cnt;					\
 	     i++, rgn = &memblock_type->regions[i])
 
-#define memblock_dbg(fmt, ...) \
-	if (memblock_debug) printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
+#define memblock_dbg(fmt, ...)						\
+	do {								\
+		if (memblock_debug)					\
+			pr_info(fmt, ##__VA_ARGS__);			\
+	} while (0)
 
 static int memblock_debug __initdata_memblock;
 static bool system_has_some_mirror __initdata_memblock = false;
_