linux-kernel - Re: [PATCH] mm: Provide consistent declaration for num_poisoned

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Date:   Mon, 26 Feb 2018 18:13:57 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH] mm: Provide consistent declaration for num_poisoned_pages

On 02/26/2018 03:57 PM, David Rientjes wrote:
> On Mon, 26 Feb 2018, Guenter Roeck wrote:
> 
>> clang reports the following compile warning.
>>
>> In file included from mm/vmscan.c:56:
>> ./include/linux/swapops.h:327:22: warning:
>> 	section attribute is specified on redeclared variable [-Wsection]
>> extern atomic_long_t num_poisoned_pages __read_mostly;
>>                       ^
>> ./include/linux/mm.h:2585:22: note: previous declaration is here
>> extern atomic_long_t num_poisoned_pages;
>>                       ^
>>
>> Let's use __read_mostly everywhere.
>>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> Cc: Matthias Kaehlcke <mka@...omium.org>
>> ---
>>   include/linux/mm.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index ad06d42adb1a..bd4bd59f02c1 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2582,7 +2582,7 @@ extern int get_hwpoison_page(struct page *page);
>>   extern int sysctl_memory_failure_early_kill;
>>   extern int sysctl_memory_failure_recovery;
>>   extern void shake_page(struct page *p, int access);
>> -extern atomic_long_t num_poisoned_pages;
>> +extern atomic_long_t num_poisoned_pages __read_mostly;
>>   extern int soft_offline_page(struct page *page, int flags);
>>   
>>   
> 
> No objection to the patch, of course, but I'm wondering if it's (1) the
> only such clang compile warning for mm/, and (2) if the re-declaration in

It is the only one I recall seeing in mm/ while testing the clang/retpoline
changes with ToT clang 7.0.0, but then I didn't pay too close attention.

> mm.h could be avoided by including swapops.h?
> 

Another alternative would be to remove the extern fom swapops.h and have
swapops.h include mm.h instead. I chose the least invasive change since
I didn't want to risk breaking some other build (after all, maybe there
was a reason for declaring num_poisoned_pages in two include files).

Guenter