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Tue, 27 Nov 2018 22:47:33 +0000 Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id wARMlWAh015141 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 27 Nov 2018 22:47:32 GMT Received: from abhmp0014.oracle.com (abhmp0014.oracle.com [141.146.116.20]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id wARMlVAB027854; Tue, 27 Nov 2018 22:47:31 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 27 Nov 2018 14:47:30 -0800 Subject: Re: [Xen-devel] [PATCH] pvcalls-front: fixes incorrect error handling To: Stefano Stabellini Cc: PanBian , Juergen Gross , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org References: <1542852432-30019-1-git-send-email-bianpan2016@163.com> <1f765e81-ed89-d110-74b1-cc8029a4555f@oracle.com> <20181127005823.GB125510@bp> <0af126ad-1a74-e4c7-d74f-658a46757b9d@oracle.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9090 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=29 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1811270189 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/27/18 4:08 PM, Stefano Stabellini wrote: > On Tue, 27 Nov 2018, Boris Ostrovsky wrote: >> On 11/27/18 3:37 PM, Stefano Stabellini wrote: >>> On Tue, 27 Nov 2018, PanBian wrote: >>>> On Mon, Nov 26, 2018 at 03:31:39PM -0500, Boris Ostrovsky wrote: >>>>> On 11/21/18 9:07 PM, Pan Bian wrote: >>>>>> kfree() is incorrectly used to release the pages allocated by >>>>>> __get_free_page() and __get_free_pages(). Use the matching deallocators >>>>>> i.e., free_page() and free_pages(), respectively. >>>>>> >>>>>> Signed-off-by: Pan Bian >>>>>> --- >>>>>> drivers/xen/pvcalls-front.c | 4 ++-- >>>>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c >>>>>> index 2f11ca7..77224d8 100644 >>>>>> --- a/drivers/xen/pvcalls-front.c >>>>>> +++ b/drivers/xen/pvcalls-front.c >>>>>> @@ -385,8 +385,8 @@ static int create_active(struct sock_mapping *map, int *evtchn) >>>>>> out_error: >>>>>> if (*evtchn >= 0) >>>>>> xenbus_free_evtchn(pvcalls_front_dev, *evtchn); >>>>>> - kfree(map->active.data.in); >>>>>> - kfree(map->active.ring); >>>>>> + free_pages((unsigned long)map->active.data.in, PVCALLS_RING_ORDER); >>>>> Is map->active.data.in guaranteed to be NULL when entering this routine? >>>> I am not sure yet. Sorry for that. I observed the mismatches between >>>> __get_free_page and kfree, and submitted the patch. >>>> >>>> But I think your consideration is reasonable. A better solution is to >>>> directly free bytes, a local variable that holds __get_free_pages return >>>> value. If you agree, I will rewrite the patch. >>> Like Boris said, map->active.ring and map->active.data.in are not >>> guaranteed to be NULL or != NULL here. For instance,map->active.ring can >>> be != NULL and map->active.data.in can be NULL. However, free_pages and >>> free_page should be able to cope with it, the same way that kfree is >>> able to cope with it? >> If map->active.data.in can be non-NULL on entry to this routine then I >> think this has been a problem all along. Pan's suggestion to use bytes >> for freeing is going to solve this (assuming bytes will be initialized >> to NULL). > Why is it a problem? map->active.data.in and map->active.ring are only > != NULL if they need to be freed. Otherwise, they are NULL. That was my question --- I wasn't sure about it, and I read your previous message as if it was possible to be calling create_active() with map->active.data.in pointing somewhere non-NULL. If it is NULL *upon entry* to calling_create() then Pan's original patch is fine. -boris > All structs > are always initialized to zero. I don't think there are any issues.