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From: Mike Christie <michael.christie@oracle.com>
To: daejun7.park@samsung.com,
	"bvanassche@acm.org" <bvanassche@acm.org>,
	"lduncan@suse.com" <lduncan@suse.com>,
	"cleech@redhat.com" <cleech@redhat.com>,
	"ming.lei@redhat.com" <ming.lei@redhat.com>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"james.bottomley@hansenpartnership.com" 
	<james.bottomley@hansenpartnership.com>
Subject: Re: [RFC PATCH 1/4] scsi: Allow drivers to set BLK_MQ_F_BLOCKING
Date: Tue, 8 Mar 2022 10:14:58 -0600	[thread overview]
Message-ID: <b70ff951-ac86-f4f8-c5f6-ff29fa184170@oracle.com> (raw)
In-Reply-To: <20220308070049epcms2p78d9e9b9bacd3fb6b52de8eb1eaedb623@epcms2p7>

On 3/8/22 1:00 AM, Daejun Park wrote:
> Hi Mike, 
> 
>> @@ -2952,8 +2954,8 @@ scsi_host_block(struct Scsi_Host *shost)
>>         }
>>
>>         /*
>> -         * SCSI never enables blk-mq's BLK_MQ_F_BLOCKING flag so
>> -         * calling synchronize_rcu() once is enough.
>> +         * Drivers that use this helper enable blk-mq's BLK_MQ_F_BLOCKING flag
>> +         * so calling synchronize_rcu() once is enough.
>>          */
>>         WARN_ON_ONCE(shost->tag_set.flags & BLK_MQ_F_BLOCKING);
> 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.

  reply	other threads:[~2022-03-08 16:15 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-08  0:39 [RFC PATCH 0/4] scsi/iscsi: Send iscsi data from kblockd Mike Christie
2022-03-08  0:39 ` [RFC PATCH 1/4] scsi: Allow drivers to set BLK_MQ_F_BLOCKING Mike Christie
2022-03-08  4:57   ` Bart Van Assche
2022-03-09  0:53   ` Ming Lei
2022-03-09  1:17     ` Mike Christie
2022-03-09  1:43       ` Ming Lei
2022-03-09 19:38         ` Mike Christie
2022-03-08  0:39 ` [RFC PATCH 2/4] scsi: iscsi: Tell drivers when we must not block Mike Christie
2022-03-08  4:59   ` Bart Van Assche
2022-03-08 15:58     ` Mike Christie
2022-03-08  0:39 ` [RFC PATCH 3/4] scsi: iscsi: Support transmit from queuecommand Mike Christie
2022-03-08  0:39 ` [RFC PATCH 4/4] scsi: iscsi_tcp: Allow user to control if " Mike Christie
2022-03-08  5:10   ` Bart Van Assche
2022-03-08 16:51     ` Mike Christie
     [not found] ` <CGME20220308004023epcas2p12ebd497c14d32f36d0aa6682c0b9d0db@epcms2p7>
2022-03-08  7:00   ` [RFC PATCH 1/4] scsi: Allow drivers to set BLK_MQ_F_BLOCKING Daejun Park
2022-03-08 16:14     ` Mike Christie [this message]
2022-03-15  8:26 ` [RFC PATCH 0/4] scsi/iscsi: Send iscsi data from kblockd Christoph Hellwig
2022-03-16  1:08   ` Ming Lei

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