From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751826AbeCUMuC (ORCPT ); Wed, 21 Mar 2018 08:50:02 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:34374 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751657AbeCUMuA (ORCPT ); Wed, 21 Mar 2018 08:50:00 -0400 Subject: Re: [PATCH 1/4] vfio: ccw: fix cleanup if cp_prefetch fails To: Dong Jia Shi , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org Cc: cohuck@redhat.com, borntraeger@de.ibm.com, pmorel@linux.vnet.ibm.com References: <20180321020822.86255-1-bjsdjshi@linux.vnet.ibm.com> <20180321020822.86255-2-bjsdjshi@linux.vnet.ibm.com> From: Halil Pasic Date: Wed, 21 Mar 2018 13:49:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180321020822.86255-2-bjsdjshi@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 18032112-0044-0000-0000-0000053E50CE X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18032112-0045-0000-0000-0000287D547B Message-Id: <682d8b1c-5aca-7015-043b-a3f1446bf378@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-03-21_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1803210156 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/21/2018 03:08 AM, Dong Jia Shi wrote: > From: Halil Pasic > > If the translation of a channel program fails, we may end up attempting > to clean up (free, unpin) stuff that never got translated (and allocated, > pinned) in the first place. > > By adjusting the lengths of the chains accordingly (so the element that > failed, and all subsequent elements are excluded) cleanup activities > based on false assumptions can be avoided. > > Let's make sure cp_free works properly after cp_prefetch returns with an > error by setting ch_len to 0 for the ccw chains those are not prefetched. This sentence used to be: Let's make sure cp_free works properly after cp_prefetch returns with an error. @Dong Jia I find the 'by setting ch_len to 0 for the ccw chains those are not prefetched' you added for clarification (I guess) somewhat problematic. The chain in which the translation failure occurred + chain->ch_len = idx; is shortened so that only the translated elements (ccws) are going to get cleaned up (on a per element basis) by cp_free. This may or may not be the first ccw. Subsequent chains are shortened to 0 as there no translation took place. So as a result of this change only properly translated ccws are going to get (re)visited by cp_free as only those may have resources bound to them which need to be released. I'm not against improving the commit message. But this ain't an improvement to me. > > Acked-by: Pierre Morel > Reviewed-by: Dong Jia Shi > Signed-off-by: Halil Pasic > Signed-off-by: Dong Jia Shi > --- > drivers/s390/cio/vfio_ccw_cp.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c > index d9a2fffd034b..2be114db02f9 100644 > --- a/drivers/s390/cio/vfio_ccw_cp.c > +++ b/drivers/s390/cio/vfio_ccw_cp.c > @@ -749,11 +749,18 @@ int cp_prefetch(struct channel_program *cp) > for (idx = 0; idx < len; idx++) { > ret = ccwchain_fetch_one(chain, idx, cp); > if (ret) > - return ret; > + goto out_err; > } > } > > return 0; > +out_err: > + /* Only cleanup the chain elements that where actually translated. */ > + chain->ch_len = idx; > + list_for_each_entry_continue(chain, &cp->ccwchain_list, next) { > + chain->ch_len = 0; > + } > + return ret; > } > > /** >