From: Ming Lei <ming.lei@redhat.com>
Date: Thu, 23 Apr 2020 10:07:13 +0800
Subject: scsi: core: Avoid calling synchronize_rcu() for each device in
scsi_host_block()
Git-commit: f983622ae60516d634008c7b1ff9ffff4f7bb8ae
Patch-mainline: v5.8-rc1
References: jsc#SLE-15152
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>
Acked-by: Lee Duncan <lduncan@suse.com>
---
drivers/scsi/scsi_lib.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 47835c4b4ee0..ff0449fbe3a0 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2841,11 +2841,27 @@ scsi_host_block(struct Scsi_Host *shost)
struct scsi_device *sdev;
int ret = 0;
+ /*
+ * Call scsi_internal_device_block_nowait so we can avoid
+ * calling synchronize_rcu() for each LUN.
+ */
shost_for_each_device(sdev, shost) {
- ret = scsi_internal_device_block(sdev);
+ mutex_lock(&sdev->state_mutex);
+ ret = scsi_internal_device_block_nowait(sdev);
+ mutex_unlock(&sdev->state_mutex);
if (ret)
break;
}
+
+ /*
+ * SCSI never enables 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);
+
+ if (!ret)
+ synchronize_rcu();
+
return ret;
}
EXPORT_SYMBOL_GPL(scsi_host_block);