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Tue, 1 Jul 2025 13:28:59 +0000 (GMT) Message-ID: <197b6dca-56be-438d-a60f-21011367c5ed@linux.ibm.com> Date: Tue, 1 Jul 2025 18:58:57 +0530 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] nbd: fix false lockdep deadlock warning To: Yu Kuai , Ming Lei Cc: josef@toxicpanda.com, axboe@kernel.dk, hch@infradead.org, hare@suse.de, linux-block@vger.kernel.org, nbd@other.debian.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, yangerkun@huawei.com, johnny.chenyi@huawei.com, "yukuai (C)" References: <20250627092348.1527323-1-yukuai1@huaweicloud.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 3za37TQSPbaaUSTfUtjGnyRhsq__BLbX X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzAxMDA4NSBTYWx0ZWRfX14L1sdyPs4d4 CCRPJ8ybBPD9qm0yx6zbRHSoDlY4ChNEdVZtxH74YFPdFOBnxiWXbVE5LtQLSEn7SvcqlFdeAmB yCsVNcKd+rtyQKc17m8/0NCkf+ifbxyFL07rpo2daQ9+Ij+y3rZjyZLvdDKHn0zubeURMIi5PQ1 sjsV3talSyqjadgCCec+G+YGdCvfO4d9XxRmzdEkLnEpfM7jS4JDAq6pdoRpRyy7Vdecxo6HtJa h5Wbuus2OmCnnWt8vpqmwuDsOa2C4AaBWSO4jSTyLyY88ABpxQqgQZ6ZwajKhmeOx8O/8ffKlbr OxslmHDt00qkxqaBSVp+QPERINjLbo36r3nP06zjlzU1uAwDp/3S9Avd4SX3suRBTjXHYF/QEVy +mwpD6pebM1+xSZFO/izk3kRT+48c2S/30/tulfCBM2Q2CoKgE1cswdgRdtK3pb4Rdft/hRn X-Authority-Analysis: v=2.4 cv=LpeSymdc c=1 sm=1 tr=0 ts=6863e2a1 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=Wb1JkmetP80A:10 a=VwQbUJbxAAAA:8 a=VxcEa7Whk2O1MWBbjpkA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: 3za37TQSPbaaUSTfUtjGnyRhsq__BLbX X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.7,FMLib:17.12.80.40 definitions=2025-07-01_02,2025-06-27_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 bulkscore=0 lowpriorityscore=0 adultscore=0 clxscore=1011 impostorscore=0 mlxscore=0 mlxlogscore=999 phishscore=0 suspectscore=0 malwarescore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2507010085 On 6/28/25 6:18 AM, Yu Kuai wrote: > Hi, > > 在 2025/06/27 19:04, Ming Lei 写道: >> I guess the patch in the following link may be simper, both two take >> similar approach: >> >> https://lore.kernel.org/linux-block/aFjbavzLAFO0Q7n1@fedora/ > > I this the above approach has concurrent problems if nbd_start_device > concurrent with nbd_start_device: > > t1: > nbd_start_device > lock > num_connections = 1 > unlock >     t2: >     nbd_add_socket >     lock >     config->num_connections++ >     unlock >         t3: >         nbd_start_device >         lock >         num_connections = 2 >         unlock >         blk_mq_update_nr_hw_queues > > blk_mq_update_nr_hw_queues > //nr_hw_queues updated to 1 before failure > return -EINVAL > In the above case, yes I see that t1 would return -EINVAL (as config->num_connections doesn't match with num_connections) but then t3 would succeed to update nr_hw_queue (as both config->num_connections and num_connections set to 2 this time). Isn't it? If yes, then the above patch (from Ming) seems good. Thanks, --Nilay