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Mon, 01 Jul 2019 20:33:14 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x61KXD4n129025; Mon, 1 Jul 2019 20:33:13 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3020.oracle.com with ESMTP id 2tebktvvnw-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 01 Jul 2019 20:33:13 +0000 Received: from abhmp0013.oracle.com (abhmp0013.oracle.com [141.146.116.19]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x61KX9KI009720; Mon, 1 Jul 2019 20:33:09 GMT Received: from [10.209.242.148] (/10.209.242.148) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 01 Jul 2019 13:33:09 -0700 Subject: Re: [PATCH net-next 2/7] net/rds: Get rid of "wait_clean_list_grace" and add locking To: Gerd Rausch , netdev@vger.kernel.org Cc: David Miller References: <5c49f180-0dbf-88b9-965d-6cb88061f31b@oracle.com> From: santosh.shilimkar@oracle.com Organization: Oracle Corporation Message-ID: <02ee3384-fccf-e7c9-8e09-49d8dc70faf3@oracle.com> Date: Mon, 1 Jul 2019 13:33:08 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <5c49f180-0dbf-88b9-965d-6cb88061f31b@oracle.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9305 signatures=668688 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 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-1907010238 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9305 signatures=668688 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1907010237 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 7/1/19 9:39 AM, Gerd Rausch wrote: > Waiting for activity on the "clean_list" to quiesce is no substitute > for proper locking. > > We can have multiple threads competing for "llist_del_first" > via "rds_ib_reuse_mr", and a single thread competing > for "llist_del_all" and "llist_del_first" via "rds_ib_flush_mr_pool". > > Since "llist_del_first" depends on "list->first->next" not to change > in the midst of the operation, simply waiting for all current calls > to "rds_ib_reuse_mr" to quiesce across all CPUs is woefully inadequate: > > By the time "wait_clean_list_grace" is done iterating over all CPUs to see > that there is no concurrent caller to "rds_ib_reuse_mr", a new caller may > have just shown up on the first CPU. > > Furthermore, explicitly calls out the need for locking: > * Cases where locking is needed: > * If we have multiple consumers with llist_del_first used in one consumer, > * and llist_del_first or llist_del_all used in other consumers, > * then a lock is needed. > > Also, while at it, drop the unused "pool" parameter > from "list_to_llist_nodes". > > Signed-off-by: Gerd Rausch > --- Looks good.