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Mon, 17 Nov 2025 11:13:13 +0000 (GMT) Message-ID: <1bd4a77f-399f-4dbe-a6b6-79b07f5e2759@linux.ibm.com> Date: Mon, 17 Nov 2025 16:43:11 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RESEND 1/5] block/blk-rq-qos: add a new helper rq_qos_add_freezed() To: Ming Lei , Yu Kuai Cc: axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, tj@kernel.org References: <20251116041024.120500-1-yukuai@fnnas.com> <20251116041024.120500-2-yukuai@fnnas.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-Authority-Analysis: v=2.4 cv=BanVE7t2 c=1 sm=1 tr=0 ts=691b034c cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=tJLSzyRPAAAA:8 a=msZIkkZUJXvqM21ySCoA:9 a=QEXdDO2ut3YA:10 a=H0xsmVfZzgdqH4_HIfU3:22 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMiBTYWx0ZWRfXxVsqVQY3fwnp L/ddHSXuwebdUBBaPnANP7kAl0NDZMRHPJsyTphZN9CdcCqufHC9Q/2xMTbeAiCkTQx+2oQrgB/ EWJjL8JQ5BRH+8CRJyTAV7X5jK0dbn4pDa6c5txvpSvM4n4oOdXe6nSA2aHgams6W1iCmskGa5z TqHAE148yqnvtQ68EONglm7nrptQQxORYjhWvmeRTdM5lrU/GbMZeIjz6v6ZHnz4xnVAeND4JH7 O8j+wXQUKHc2XdMrcKcRc0BZKxCOutqLiBylmJvbMTml6WA3Fgpt3XNg9ZhMZOcCWft1vuSAgPI y/dsnvAJvDB3JzgKADq+ar+5kobnLptU7ENDiG1V0I3a6j9X8pzWcYRLWmTvctZK93Qp1nC9VAa /6fDPjKK2zFM4xpQGph+6xmCB3jb0Q== X-Proofpoint-GUID: P8xELGG2g3yOani_Cylg3lh7-TzqAE2R X-Proofpoint-ORIG-GUID: P8xELGG2g3yOani_Cylg3lh7-TzqAE2R X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-17_02,2025-11-13_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 lowpriorityscore=0 suspectscore=0 spamscore=0 impostorscore=0 priorityscore=1501 clxscore=1015 phishscore=0 bulkscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511150032 On 11/17/25 4:31 PM, Ming Lei wrote: > On Sun, Nov 16, 2025 at 12:10:20PM +0800, Yu Kuai wrote: >> queue should not be freezed under rq_qos_mutex, see example index >> commit 9730763f4756 ("block: correct locking order for protecting blk-wbt >> parameters"), which means current implementation of rq_qos_add() is >> problematic. Add a new helper and prepare to fix this problem in >> following patches. >> >> Signed-off-by: Yu Kuai >> --- >> block/blk-rq-qos.c | 27 +++++++++++++++++++++++++++ >> block/blk-rq-qos.h | 2 ++ >> 2 files changed, 29 insertions(+) >> >> diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c >> index 654478dfbc20..353397d7e126 100644 >> --- a/block/blk-rq-qos.c >> +++ b/block/blk-rq-qos.c >> @@ -322,6 +322,33 @@ void rq_qos_exit(struct request_queue *q) >> mutex_unlock(&q->rq_qos_mutex); >> } >> >> +int rq_qos_add_freezed(struct rq_qos *rqos, struct gendisk *disk, >> + enum rq_qos_id id, const struct rq_qos_ops *ops) >> +{ >> + struct request_queue *q = disk->queue; >> + >> + WARN_ON_ONCE(q->mq_freeze_depth == 0); >> + lockdep_assert_held(&q->rq_qos_mutex); >> + >> + if (rq_qos_id(q, id)) >> + return -EBUSY; >> + >> + rqos->disk = disk; >> + rqos->id = id; >> + rqos->ops = ops; >> + rqos->next = q->rq_qos; >> + q->rq_qos = rqos; >> + blk_queue_flag_set(QUEUE_FLAG_QOS_ENABLED, q); >> + >> + if (rqos->ops->debugfs_attrs) { >> + mutex_lock(&q->debugfs_mutex); >> + blk_mq_debugfs_register_rqos(rqos); >> + mutex_unlock(&q->debugfs_mutex); >> + } > > It will cause more lockdep splat to let q->debugfs_mutex depend on queue freeze, > I think we already have that ->debugfs_mutex dependency on ->freeze_lock. for instance, ioc_qos_write => freeze-queue blk_iocost_init rq_qos_add and also, queue_wb_lat_store => freeze-queue wbt_init rq_qos_add > Also blk_mq_debugfs_register_rqos() does _not_ require queue to be frozen, > and it should be fine to move blk_mq_debugfs_register_rqos() out of queue > freeze. > Yes correct, but I thought this pacthset is meant only to address incorrect locking order between ->rq_qos_mutex and ->freeze_lock. So do you suggest also refactoring code to avoid ->debugfs_mutex dependency on ->freeze_lock? If yes then shouldn't that be handled in a separate patchset? Thanks, --Nilay