From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A7B4F3D97C; Wed, 20 Dec 2023 15:02:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=kernel.org X-IronPort-AV: E=McAfee;i="6600,9927,10930"; a="3044485" X-IronPort-AV: E=Sophos;i="6.04,291,1695711600"; d="scan'208";a="3044485" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Dec 2023 07:02:04 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10930"; a="920005433" X-IronPort-AV: E=Sophos;i="6.04,291,1695711600"; d="scan'208";a="920005433" Received: from smile.fi.intel.com ([10.237.72.54]) by fmsmga001.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Dec 2023 07:02:02 -0800 Received: from andy by smile.fi.intel.com with local (Exim 4.97) (envelope-from ) id 1rFy1q-00000007ZA3-1w1S; Wed, 20 Dec 2023 16:58:34 +0200 Date: Wed, 20 Dec 2023 16:58:34 +0200 From: Andy Shevchenko To: Kent Gibson Cc: linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org, brgl@bgdev.pl, linus.walleij@linaro.org Subject: Re: [PATCH 2/4] gpiolib: cdev: allocate linereq using kvzalloc() Message-ID: References: <20231220015106.16732-1-warthog618@gmail.com> <20231220015106.16732-3-warthog618@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo On Wed, Dec 20, 2023 at 10:53:07PM +0800, Kent Gibson wrote: > On Wed, Dec 20, 2023 at 04:30:24PM +0200, Andy Shevchenko wrote: > > On Wed, Dec 20, 2023 at 09:51:04AM +0800, Kent Gibson wrote: > > > The size of struct linereq may exceed a page, so allocate space for > > > it using kvzalloc() instead of kzalloc(). > > > > It might be this needs a bit of elaboration. The kmalloc() tries to allocate > > a contiguous (in physical address space) chunk of memory and with fragmented > > memory it might be not possible. So the above issue might (rarely) happen. > > In most cases the call to kmalloc() will succeed. > > For sure, the kzalloc() generally works - or we wouldn't've gotten this > far as tests with MAX_LINES would've been failing. > We are targetting a very niche failure mode here. > > The size allocated can only be determined at runtime, may be more or > less than a page, and we don't care whether the physical memory allocated > is contiguous. > As such kvzalloc() is the appropriate allocator. > > Are you suggesting repeating the relevant sections of the > kmalloc/vmalloc() documentation or Memory Allocation Guide as part of the > checkin comment? I suggesting to make clear in the commit message that: - there is no bug per se with the code logic (i.o.w. there is no issue to have allocations bigger than one page) - this is very rarely case when it might be a problem You can also put a reference to the documentation, if you wish. This should be harmless and adding not more than a line into the commit message (or even as a Link: tag to the HTML variant of it). -- With Best Regards, Andy Shevchenko