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([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id a6-20020a056808120600b003874631e249sm944134oil.36.2023.04.06.11.23.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Apr 2023 11:23:32 -0700 (PDT) Message-ID: <1ed73bf7-809f-74e8-559d-e240a2a291c8@roeck-us.net> Date: Thu, 6 Apr 2023 11:23:30 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH] mm-treewide-redefine-max_order-sanely-fix.txt Content-Language: en-US To: "Kirill A. Shutemov" , Mike Rapoport Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <9460377a-38aa-4f39-ad57-fb73725f92db@roeck-us.net> <20230406072529.vupqyrzqnhyozeyh@box.shutemov.name> <83e6bc46-dfc0-0e95-e69c-5b996af1e50b@roeck-us.net> <20230406151015.yndcm24fyxitvqyc@box.shutemov.name> From: Guenter Roeck In-Reply-To: <20230406151015.yndcm24fyxitvqyc@box.shutemov.name> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0774C120009 X-Rspam-User: X-Stat-Signature: u3owutwe9chngh8w3at7g6w6cp4jfb7p X-HE-Tag: 1680805413-943082 X-HE-Meta: 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 He/Tbm8G 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 4/6/23 08:10, Kirill A. Shutemov wrote: > On Thu, Apr 06, 2023 at 06:57:41AM -0700, Guenter Roeck wrote: >> On 4/6/23 00:25, Kirill A. Shutemov wrote: >>> On Wed, Apr 05, 2023 at 10:20:26PM -0700, Guenter Roeck wrote: >>>> Hi, >>>> >>>> On Wed, Mar 15, 2023 at 06:38:00PM +0300, Kirill A. Shutemov wrote: >>>>> fix min() warning >>>>> >>>>> Link: https://lkml.kernel.org/r/20230315153800.32wib3n5rickolvh@box >>>>> Reported-by: kernel test robot >>>>> Link: https://lore.kernel.org/oe-kbuild-all/202303152343.D93IbJmn-lkp@intel.com/ >>>>> Signed-off-by: "Kirill A. Shutemov" >>>>> Cc: "Kirill A. Shutemov" >>>>> Cc: Zi Yan >>>>> Signed-off-by: Andrew Morton >>>> >>>> This patch results in various boot failures (hang) on arm targets >>>> in linux-next. Debug messages reveal the reason. >>>> >>>> ########### MAX_ORDER=10 start=0 __ffs(start)=-1 min()=10 min_t=-1 >>>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >>>> >>>> If start==0, __ffs(start) returns 0xfffffff or (as int) -1, which min_t() >>>> interprets as such, while min() apparently uses the returned unsigned long >>>> value. Obviously a negative order isn't received well by the rest of the >>>> code. >>> >>> Actually, __ffs() is not defined for 0. >>> >>> Maybe something like this? >>> >>> diff --git a/mm/memblock.c b/mm/memblock.c >>> index 7911224b1ed3..63603b943bd0 100644 >>> --- a/mm/memblock.c >>> +++ b/mm/memblock.c >>> @@ -2043,7 +2043,11 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end) >>> int order; >>> while (start < end) { >>> - order = min_t(int, MAX_ORDER, __ffs(start)); >>> + /* __ffs() behaviour is undefined for 0 */ >>> + if (start) >>> + order = min_t(int, MAX_ORDER, __ffs(start)); >>> + else >>> + order = MAX_ORDER; >> >> Shouldn't that be >> else >> order = 0; >> ? > > +Mike. > > No. start == 0 is MAX_ORDER-aligned. We want to free the pages in the > largest chunks alignment allows. > Ah, ok. Makes sense. Thanks, Guenter