From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id E8DB96B0033 for ; Fri, 15 Dec 2017 13:01:21 -0500 (EST) Received: by mail-pg0-f70.google.com with SMTP id a13so7503315pgt.0 for ; Fri, 15 Dec 2017 10:01:21 -0800 (PST) Received: from out0-201.mail.aliyun.com (out0-201.mail.aliyun.com. [140.205.0.201]) by mx.google.com with ESMTPS id c7si5310487plr.486.2017.12.15.10.01.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 15 Dec 2017 10:01:20 -0800 (PST) Subject: Re: [PATCH] mm: thp: avoid uninitialized variable use References: <20171215125129.2948634-1-arnd@arndb.de> From: "Yang Shi" Message-ID: <8d5476e2-5f87-1134-62d4-9f649c4e709a@alibaba-inc.com> Date: Sat, 16 Dec 2017 02:01:08 +0800 MIME-Version: 1.0 In-Reply-To: <20171215125129.2948634-1-arnd@arndb.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Arnd Bergmann , Andrew Morton , Michal Hocko , "Kirill A. Shutemov" Cc: Stephen Rothwell , Vlastimil Babka , David Rientjes , Ingo Molnar , linux-mm@kvack.org, linux-kernel@vger.kernel.org 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. Regards, Yang > > Presumable we are not supposed to call find_vma() without the mmap_sem > either, so setting it to NULL for this case seems appropriate. > > Fixes: 0951b59acf3a ("mm: thp: use down_read_trylock() in khugepaged to avoid long block") > Signed-off-by: Arnd Bergmann > --- > I'm not completely sure this patch is sufficient, it gets rid of > the warning, but it would be good to have the code reviewed better > to see if other problems remain that result from down_read_trylock() > patch. > --- > mm/khugepaged.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 521b908f9600..b7e2268dfc9a 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1677,11 +1677,10 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, > * Don't wait for semaphore (to avoid long wait times). Just move to > * the next mm on the list. > */ > + vma = NULL; > if (unlikely(!down_read_trylock(&mm->mmap_sem))) > goto breakouterloop_mmap_sem; > - if (unlikely(khugepaged_test_exit(mm))) > - vma = NULL; > - else > + if (likely(!khugepaged_test_exit(mm))) > vma = find_vma(mm, khugepaged_scan.address); > > progress++; > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org