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Tue, 15 Apr 2025 09:39:13 +0000 (GMT) Message-ID: Date: Tue, 15 Apr 2025 15:09:12 +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 11/15] block: move elv_register[unregister]_queue out of elevator_lock To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Shinichiro Kawasaki , =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Christoph Hellwig References: <20250410133029.2487054-1-ming.lei@redhat.com> <20250410133029.2487054-12-ming.lei@redhat.com> <43e99891-94f2-4b31-a073-f7e717afbdd7@linux.ibm.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: hPFfwOk92OUMBXiVOSUCcCYIpv0E6nzU X-Proofpoint-ORIG-GUID: hPFfwOk92OUMBXiVOSUCcCYIpv0E6nzU X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1095,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-04-15_04,2025-04-10_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 phishscore=0 clxscore=1015 mlxlogscore=697 adultscore=0 lowpriorityscore=0 malwarescore=0 impostorscore=0 suspectscore=0 mlxscore=0 bulkscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502280000 definitions=main-2504150066 On 4/14/25 6:54 AM, Ming Lei wrote: > On Sat, Apr 12, 2025 at 12:50:10AM +0530, Nilay Shroff wrote: >> >> >> On 4/10/25 7:00 PM, Ming Lei wrote: >>> +int elevator_change_done(struct request_queue *q, struct elev_change_ctx *ctx) >>> +{ >>> + int ret = 0; >>> + >>> + if (ctx->old) { >>> + elv_unregister_queue(q, ctx->old); >>> + kobject_put(&ctx->old->kobj); >>> + } >>> + if (ctx->new) { >>> + ret = elv_register_queue(q, ctx->new, ctx->uevent); >>> + if (ret) { >>> + unsigned memflags = blk_mq_freeze_queue(q); >>> + >>> + mutex_lock(&q->elevator_lock); >>> + elevator_exit(q); >>> + mutex_unlock(&q->elevator_lock); >>> + blk_mq_unfreeze_queue(q, memflags); >>> + } >>> + } >>> + return 0; >>> +} >>> + >> We could have sysf elevator attributes simultaneously accessed while this function >> adds/removes sysfs elevator attributes without any protection. In fact, the show/store >> methods of elevator attributes runs with e->sysfs_lock held. So it seems moving >> the above function out of lock protection might cause crash or other side effects? > > sysfs/kobject provides such protection, and kobject_del() will drain any > in-flight attribute access. > Okay, so in that case do we now really need e->sysfs_lock protection while accessing elevator attributes? Thanks, --Nilay