From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) (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 560CD7F0 for ; Wed, 1 Mar 2023 01:56:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1677635775; x=1709171775; h=message-id:date:mime-version:cc:subject:to:references: from:in-reply-to:content-transfer-encoding; bh=JvUgqcrgfQlznLASCJxhJivg+YLodSnLHw0JHLUxNf0=; b=Ai451P0FkiurqhI1GqtLt9dxiki1O8UNxmGbu92aOB3KfL03U6VjIbCB N/N6QZBYJ9bjdl4FuU/gFw0qQxMXf6VcTxn2La0zp5UQ93XxGjnTLEtdF NtrCKrI1K/pggJi2SiVQpkvdYRvDP1j6UOis0MT/MuY6ZFW/xhdS92/OV XxRmcwOTyRveM9I7MKD0BGfS/8nw4qaz9Xfose8hQCfdJvNBrX5nvF1iK zhyZW7kBkvr/PCNOR+0t+lHEgZ/V1PRotwpTuyaCgXUrLTlX1DmNstg9j lyOk4v2NcmLLVW+jAqAjQfV80t6YXzmJldS/SSksjQZw/NpeV1EL7l4cY Q==; X-IronPort-AV: E=McAfee;i="6500,9779,10635"; a="336590408" X-IronPort-AV: E=Sophos;i="5.98,223,1673942400"; d="scan'208";a="336590408" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Feb 2023 17:56:14 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10635"; a="651828038" X-IronPort-AV: E=Sophos;i="5.98,223,1673942400"; d="scan'208";a="651828038" Received: from allen-box.sh.intel.com (HELO [10.239.159.48]) ([10.239.159.48]) by orsmga006.jf.intel.com with ESMTP; 28 Feb 2023 17:56:12 -0800 Message-ID: <91e8d0ee-ee28-0866-85c9-2b499a5dcc38@linux.intel.com> Date: Wed, 1 Mar 2023 09:55:21 +0800 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Cc: baolu.lu@linux.intel.com, iommu@lists.linux.dev, Kevin Tian , linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, Nicolin Chen , Yi Liu Subject: Re: [PATCH 09/14] iommufd: Add iommufd_device_replace() To: Jason Gunthorpe References: <9-v1-7612f88c19f5+2f21-iommufd_alloc_jgg@nvidia.com> Content-Language: en-US From: Baolu Lu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/28/23 9:51 PM, Jason Gunthorpe wrote: > On Tue, Feb 28, 2023 at 09:50:52AM +0800, Baolu Lu wrote: >> On 2/27/23 9:58 PM, Jason Gunthorpe wrote: >>> On Sun, Feb 26, 2023 at 11:01:59AM +0800, Baolu Lu wrote: >>>> On 2/25/23 8:27 AM, Jason Gunthorpe wrote: >>>>> @@ -437,25 +517,77 @@ int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id) >>>>> struct iommufd_ioas *ioas = >>>>> container_of(pt_obj, struct iommufd_ioas, obj); >>>>> - rc = iommufd_device_auto_get_domain(idev, ioas, pt_id); >>>>> - if (rc) >>>>> + destroy_hwpt = iommufd_device_auto_get_domain(idev, ioas, pt_id, >>>>> + do_attach); >>>>> + if (IS_ERR(destroy_hwpt)) >>>>> goto out_put_pt_obj; >>>>> break; >>>>> } >>>>> default: >>>>> - rc = -EINVAL; >>>>> + destroy_hwpt = ERR_PTR(-EINVAL); >>>>> goto out_put_pt_obj; >>>>> } >>>>> + iommufd_put_object(pt_obj); >>>>> - refcount_inc(&idev->obj.users); >>>>> - rc = 0; >>>>> + /* This destruction has to be after we unlock everything */ >>>>> + if (destroy_hwpt) >>>> Should this be >>>> >>>> if (!IS_ERR_OR_NULL(destroy_hwpt)) >>>> >>>> ? >>> Never use IS_ERR_OR_NULL .. >> Can you please elaborate a bit on this? I can still see a lot of use of >> it in the tree. > Yes, sadly. It is usually some signal of toxic confusion about what > things mean. > > A function that returns an ERR_PTR should very rarely return NULL, and > if it does return NULL then NULL wasn't an error. That's true. > Further you should never store an ERR_PTR in some structure and then > later try to test it, that is madness. > > So with properly structured code the need should not exist. > > https://lore.kernel.org/all/20130109150427.GL3931@n2100.arm.linux.org.uk/ It's clear to me now. Thanks a lot for the explanation. Best regards, baolu