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From: "Yang Shi" <yang.s@alibaba-inc.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Vlastimil Babka <vbabka@suse.cz>,
	David Rientjes <rientjes@google.com>,
	Ingo Molnar <mingo@kernel.org>, Linux-MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: thp: avoid uninitialized variable use
Date: Sun, 17 Dec 2017 06:25:17 +0800	[thread overview]
Message-ID: <63b69d2b-1c1d-6f08-30a6-e996b6842000@alibaba-inc.com> (raw)
In-Reply-To: <CAK8P3a3arg08JuBrz+Pqa47xsFCHtxTJ+7ywepeJpJro02NEjg@mail.gmail.com>



On 12/16/17 4:24 AM, Arnd Bergmann wrote:
> On Fri, Dec 15, 2017 at 7:01 PM, Yang Shi <yang.s@alibaba-inc.com> wrote:
>>
>>
>> On 12/15/17 4:51 AM, Arnd Bergmann wrote:
>>>
>>> When the down_read_trylock() fails, 'vma' has not been initialized
>>> yet, which gcc now warns about:
>>>
>>> mm/khugepaged.c: In function 'khugepaged':
>>> mm/khugepaged.c:1659:25: error: 'vma' may be used uninitialized in this
>>> function [-Werror=maybe-uninitialized]
>>
>>
>> Arnd,
>>
>> Thanks for catching this. I'm wondering why my test didn't catch it. It
>> might be because my gcc is old. I'm using gcc 4.8.5 on centos 7.
> 
> Correct, gcc-4.8 and earlier have too many false-positive warnings with
> -Wmaybe-uninitialized, so we turn it off on those versions. 4.9 is much
> better here, but I'd recommend using gcc-6 or gcc-7 when you upgrade,
> they have a much better set of default warnings besides producing better
> binary code.

Thanks, I just upgraded gcc to 6.4 on my cetnos 7 machine. But, I ran 
into a build error with 4.15-rc3 kernel, but 4.14 is fine. I bisected to 
a commit in Makefile. I will email my bug report to the mailing list.

Regards,
Yang

> 
> See http://git.infradead.org/users/segher/buildall.git for a simple way
> to build toolchains suitable for building kernels in varying architectures
> and versions.
> 
>         Arnd
> 

WARNING: multiple messages have this Message-ID (diff)
From: "Yang Shi" <yang.s@alibaba-inc.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Vlastimil Babka <vbabka@suse.cz>,
	David Rientjes <rientjes@google.com>,
	Ingo Molnar <mingo@kernel.org>, Linux-MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: thp: avoid uninitialized variable use
Date: Sun, 17 Dec 2017 06:25:17 +0800	[thread overview]
Message-ID: <63b69d2b-1c1d-6f08-30a6-e996b6842000@alibaba-inc.com> (raw)
In-Reply-To: <CAK8P3a3arg08JuBrz+Pqa47xsFCHtxTJ+7ywepeJpJro02NEjg@mail.gmail.com>



On 12/16/17 4:24 AM, Arnd Bergmann wrote:
> On Fri, Dec 15, 2017 at 7:01 PM, Yang Shi <yang.s@alibaba-inc.com> wrote:
>>
>>
>> On 12/15/17 4:51 AM, Arnd Bergmann wrote:
>>>
>>> When the down_read_trylock() fails, 'vma' has not been initialized
>>> yet, which gcc now warns about:
>>>
>>> mm/khugepaged.c: In function 'khugepaged':
>>> mm/khugepaged.c:1659:25: error: 'vma' may be used uninitialized in this
>>> function [-Werror=maybe-uninitialized]
>>
>>
>> Arnd,
>>
>> Thanks for catching this. I'm wondering why my test didn't catch it. It
>> might be because my gcc is old. I'm using gcc 4.8.5 on centos 7.
> 
> Correct, gcc-4.8 and earlier have too many false-positive warnings with
> -Wmaybe-uninitialized, so we turn it off on those versions. 4.9 is much
> better here, but I'd recommend using gcc-6 or gcc-7 when you upgrade,
> they have a much better set of default warnings besides producing better
> binary code.

Thanks, I just upgraded gcc to 6.4 on my cetnos 7 machine. But, I ran 
into a build error with 4.15-rc3 kernel, but 4.14 is fine. I bisected to 
a commit in Makefile. I will email my bug report to the mailing list.

Regards,
Yang

> 
> See http://git.infradead.org/users/segher/buildall.git for a simple way
> to build toolchains suitable for building kernels in varying architectures
> and versions.
> 
>         Arnd
> 

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  reply	other threads:[~2017-12-16 22:25 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-15 12:51 [PATCH] mm: thp: avoid uninitialized variable use Arnd Bergmann
2017-12-15 12:51 ` Arnd Bergmann
2017-12-15 13:03 ` Michal Hocko
2017-12-15 13:03   ` Michal Hocko
2017-12-15 18:01 ` Yang Shi
2017-12-15 18:01   ` Yang Shi
2017-12-16 12:24   ` Arnd Bergmann
2017-12-16 12:24     ` Arnd Bergmann
2017-12-16 22:25     ` Yang Shi [this message]
2017-12-16 22:25       ` Yang Shi

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