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Tue, 8 Mar 2022 16:15:00 +0000 Received: from DM5PR10MB1466.namprd10.prod.outlook.com ([fe80::3dd8:6b8:e2e6:c3a2]) by DM5PR10MB1466.namprd10.prod.outlook.com ([fe80::3dd8:6b8:e2e6:c3a2%12]) with mapi id 15.20.5038.027; Tue, 8 Mar 2022 16:15:00 +0000 Message-ID: Date: Tue, 8 Mar 2022 10:14:58 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [RFC PATCH 1/4] scsi: Allow drivers to set BLK_MQ_F_BLOCKING Content-Language: en-US To: daejun7.park@samsung.com, "bvanassche@acm.org" , "lduncan@suse.com" , "cleech@redhat.com" , "ming.lei@redhat.com" , "martin.petersen@oracle.com" , "linux-scsi@vger.kernel.org" , "james.bottomley@hansenpartnership.com" References: <20220308003957.123312-2-michael.christie@oracle.com> <20220308003957.123312-1-michael.christie@oracle.com> <20220308070049epcms2p78d9e9b9bacd3fb6b52de8eb1eaedb623@epcms2p7> From: Mike Christie In-Reply-To: <20220308070049epcms2p78d9e9b9bacd3fb6b52de8eb1eaedb623@epcms2p7> Content-Type: text/plain; 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> Should we keep this line? > > And I think scsi_host_block() should call synchronize_srcu() rather than > synchronize_rcu(), if the BLK_MQ_F_BLOCKING flag is used. > Sorry, I messed up the comment. The comment should have been: Drivers that set the blk-mq BLK_MQ_F_BLOCKING do not use this function so calling synchronize_rcu() once is enough. -------------------------- The iscsi drivers that use BLK_MQ_F_BLOCKING use scsi_target_block which ends up calling blk_mq_wait_quiesce_done. That function will do the right thing wrt rcu/srcu based on if the BLK_MQ_F_BLOCKING flag was set when the scsi host was added. So in the above comment I meant to express drivers that use BLK_MQ_F_BLOCKING shouldn't call scsi_host_block and right now the WARN call is valid. However, I could do something like you are suggesting and do a: if (shost->hostt->queuecommand_may_sleep_blocks) synchronize_srcu() else synchronize_rcu() However, I don't have any way to test it, so I was a little reluctant to add that.