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Tue, 07 Apr 2020 19:52:14 -0700 Subject: Re: [PATCH net 2/2] net/rds: Fix MR reference counting problem To: zerons , Ka-Cheong Poon , netdev@vger.kernel.org Cc: davem@davemloft.net, rds-devel@oss.oracle.com References: <4b96ea99c3f0ccd5cc0683a5c944a1c4da41cc38.1586275373.git.ka-cheong.poon@oracle.com> <96f17f7d-365c-32ec-2efe-a6a5d9d306b7@oracle.com> From: santosh.shilimkar@oracle.com Organization: Oracle Corporation Message-ID: <8db99ccf-d762-8ec6-5439-732ad5b30f8e@oracle.com> Date: Tue, 7 Apr 2020 19:52:13 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9584 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 mlxlogscore=999 mlxscore=0 priorityscore=1501 bulkscore=0 adultscore=0 impostorscore=0 phishscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004080016 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 4/7/20 7:25 PM, zerons wrote: > On 4/8/20 03:30, santosh.shilimkar@oracle.com wrote: >> On 4/7/20 9:08 AM, Ka-Cheong Poon wrote: >>> In rds_free_mr(), it calls rds_destroy_mr(mr) directly.  But this >>> defeats the purpose of reference counting and makes MR free handling >>> impossible.  It means that holding a reference does not guarantee that >>> it is safe to access some fields.  For example, In >>> rds_cmsg_rdma_dest(), it increases the ref count, unlocks and then >>> calls mr->r_trans->sync_mr().  But if rds_free_mr() (and >>> rds_destroy_mr()) is called in between (there is no lock preventing >>> this to happen), r_trans_private is set to NULL, causing a panic. >>> Similar issue is in rds_rdma_unuse(). >>> >>> Reported-by: zerons >>> Signed-off-by: Ka-Cheong Poon >>> --- >> Thanks for getting this out on the list. >> >> Hi zerons, >> Can you please review it and see it addresses your concern ? >> > > Yes, the MR gets freed only when the ref count decreases to zero does > address my concern. I think it make the logic cleaner as well. Fantastic! > Thanks for confirmation. FWIW, Acked-by: Santosh Shilimkar