[PATCH v4 15/17] scsi: ufs: Stop using the clock scaling lock in the error handler

[Bart Van Assche <bvanassche@acm.org>]

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.

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Tested-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/ufs/ufshcd.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index d434d76aa657..9f0a1f637030 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/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);
 }