scsi: ufs: Stop using the clock scaling lock in the error handler

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.

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>

drivers/scsi/ufs/ufshcd.c

@@ -2684,6 +2684,12 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
 	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:
 		break;
@@ -2762,7 +2768,10 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
 	}
 
 	ufshcd_send_command(hba, tag);
+
 out:
+	rcu_read_unlock();
+
 	up_read(&hba->clk_scaling_lock);
 
 	if (ufs_trigger_eh()) {
@@ -5951,8 +5960,7 @@ static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
 	}
 	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);
 }