From: Bart Van Assche <bvanassche@acm.org>
Date: Fri, 3 Dec 2021 15:19:48 -0800
Subject: scsi: ufs: Stop using the clock scaling lock in the error handler
Git-commit: 5675c381ea51360b4968b78f23aefda73e3de90d
Patch-mainline: v5.17-rc1
References: git-fixes

Instead of locking and unlocking the clock scaling lock, surround the
command queueing code with an RCU reader lock and call synchronize_rcu().
This patch prepares for removal of the clock scaling lock.

[lduncan: refreshed to apply.]

Link: https://lore.kernel.org/r/20211203231950.193369-16-bvanassche@acm.org
Tested-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Lee Duncan <lduncan@suse.com>
---
 drivers/scsi/ufs/ufshcd.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -2717,6 +2717,12 @@ static int ufshcd_queuecommand(struct Sc
 	if (!down_read_trylock(&hba->clk_scaling_lock))
 		return SCSI_MLQUEUE_HOST_BUSY;
 
+	/*
+	 * Allows the UFS error handler to wait for prior ufshcd_queuecommand()
+	 * calls.
+	 */
+	rcu_read_lock();
+
 	switch (hba->ufshcd_state) {
 	case UFSHCD_STATE_OPERATIONAL:
 	case UFSHCD_STATE_EH_SCHEDULED_NON_FATAL:
@@ -2789,7 +2795,10 @@ static int ufshcd_queuecommand(struct Sc
 	wmb();
 
 	ufshcd_send_command(hba, tag);
+
 out:
+	rcu_read_unlock();
+
 	up_read(&hba->clk_scaling_lock);
 	return err;
 }
@@ -5929,8 +5938,7 @@ static void ufshcd_err_handling_prepare(
 	}
 	ufshcd_scsi_block_requests(hba);
 	/* Drain ufshcd_queuecommand() */
-	down_write(&hba->clk_scaling_lock);
-	up_write(&hba->clk_scaling_lock);
+	synchronize_rcu();
 	cancel_work_sync(&hba->eeh_work);
 }