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scsi: core: Avoid calling synchronize_rcu() for each device in scsi_host_block()
scsi_host_block() calls scsi_internal_device_block() for each scsi_device and scsi_internal_device_block() calls blk_mq_quiesce_queue() for each LUN. Since synchronize_rcu() is called from blk_mq_quiesce_queue(), this can cause substantial slowdowns on systems with many LUNs. Use scsi_internal_device_block_nowait() to implement scsi_host_block() so it is sufficient to run synchronize_rcu() once. This is safe since SCSI does not set the BLK_MQ_F_BLOCKING flag. [mkp: commit desc and comment tweaks] Link: https://lore.kernel.org/r/20200423020713.332743-1-ming.lei@redhat.com Cc: Steffen Maier <maier@linux.ibm.com> Cc: Bart Van Assche <bvanassche@acm.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Dexuan Cui <decui@microsoft.com> Cc: Hannes Reinecke <hare@suse.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Hannes Reinecke <hare@suse.de> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
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@ -2841,11 +2841,27 @@ scsi_host_block(struct Scsi_Host *shost)
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struct scsi_device *sdev;
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int ret = 0;
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/*
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* Call scsi_internal_device_block_nowait so we can avoid
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* calling synchronize_rcu() for each LUN.
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*/
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shost_for_each_device(sdev, shost) {
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ret = scsi_internal_device_block(sdev);
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mutex_lock(&sdev->state_mutex);
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ret = scsi_internal_device_block_nowait(sdev);
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mutex_unlock(&sdev->state_mutex);
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if (ret)
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break;
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}
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/*
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* SCSI never enables blk-mq's BLK_MQ_F_BLOCKING flag so
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* calling synchronize_rcu() once is enough.
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*/
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WARN_ON_ONCE(shost->tag_set.flags & BLK_MQ_F_BLOCKING);
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if (!ret)
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synchronize_rcu();
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return ret;
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}
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EXPORT_SYMBOL_GPL(scsi_host_block);
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