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Thu, 6 Apr 2023 11:10:18 -0400 (EDT) Received: by box.shutemov.name (Postfix, from userid 1000) id 13781109B00; Thu, 6 Apr 2023 18:10:15 +0300 (+03) Date: Thu, 6 Apr 2023 18:10:15 +0300 From: "Kirill A. Shutemov" To: Guenter Roeck , Mike Rapoport Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm-treewide-redefine-max_order-sanely-fix.txt Message-ID: <20230406151015.yndcm24fyxitvqyc@box.shutemov.name> References: <9460377a-38aa-4f39-ad57-fb73725f92db@roeck-us.net> <20230406072529.vupqyrzqnhyozeyh@box.shutemov.name> <83e6bc46-dfc0-0e95-e69c-5b996af1e50b@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <83e6bc46-dfc0-0e95-e69c-5b996af1e50b@roeck-us.net> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A01AC2001D X-Stat-Signature: th1wocp1hmnbgy94arstpsc3qbswuyy7 X-HE-Tag: 1680793819-478812 X-HE-Meta: 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 /9lyiUhm 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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 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. -- Kiryl Shutsemau / Kirill A. Shutemov