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Thu, 10 Apr 2025 19:20:43 +0000 (GMT) Message-ID: Date: Fri, 11 Apr 2025 00:50:42 +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 15/15] block: move wbt_enable_default() out of queue freezing from scheduler's ->exit() To: Ming Lei , Jens Axboe , linux-block@vger.kernel.org Cc: Shinichiro Kawasaki , =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Christoph Hellwig References: <20250410133029.2487054-1-ming.lei@redhat.com> <20250410133029.2487054-16-ming.lei@redhat.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20250410133029.2487054-16-ming.lei@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: T2zOuOD9_w8--fjbLpvCdLjHOk3K46WA X-Proofpoint-ORIG-GUID: T2zOuOD9_w8--fjbLpvCdLjHOk3K46WA 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=2025-04-10_05,2025-04-10_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 suspectscore=0 mlxscore=0 priorityscore=1501 adultscore=0 phishscore=0 mlxlogscore=999 impostorscore=0 bulkscore=0 clxscore=1015 lowpriorityscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502280000 definitions=main-2504100133 On 4/10/25 7:00 PM, Ming Lei wrote: > scheduler's ->exit() is called with queue frozen and elevator lock is held, and > wbt_enable_default() can't be called with queue frozen, otherwise the > following lockdep warning is triggered: > > #6 (&q->rq_qos_mutex){+.+.}-{4:4}: > #5 (&eq->sysfs_lock){+.+.}-{4:4}: > #4 (&q->elevator_lock){+.+.}-{4:4}: > #3 (&q->q_usage_counter(io)#3){++++}-{0:0}: > #2 (fs_reclaim){+.+.}-{0:0}: > #1 (&sb->s_type->i_mutex_key#3){+.+.}-{4:4}: > #0 (&q->debugfs_mutex){+.+.}-{4:4}: > > Fix the issue by moving wbt_enable_default() out of bfq's exit(), and > call it from elevator_change_done(). [...] > diff --git a/block/elevator.c b/block/elevator.c > index 1cc640a9db3e..9cf78db4d6a4 100644 > --- a/block/elevator.c > +++ b/block/elevator.c > @@ -676,8 +676,13 @@ int elevator_change_done(struct request_queue *q, struct elev_change_ctx *ctx) > int ret = 0; > > if (ctx->old) { > + bool enable_wbt = test_bit(ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT, > + &ctx->old->flags); > + > elv_unregister_queue(q, ctx->old); > kobject_put(&ctx->old->kobj); > + if (enable_wbt) > + wbt_enable_default(q->disk); > } wbt_enable_default is also called from ioc_qos_write and blk_register_queue with ->elevator_lock protection. So avoiding protection here doesn't seem correct. Thanks, --Nilay