[PATCH RFC 4/6] scsi: ufs: Fix a possible dead lock in clock scaling

[Adrian Hunter <adrian.hunter@intel.com>]

Instead of downgrade_write(), extend the ufshcd_down_write() to cover
ufshcd_wb_toggle() because ufshcd_down_write() now supports nesting
ufshcd_down_read() but down_read() nested within down_read() can deadlock.

Reported-by: Can Guo <cang@codeaurora.org>
Link: https://lore.kernel.org/all/fbc4d03a07f03fe4fbe697813111471f@codeaurora.org
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 drivers/scsi/ufs/ufshcd.c | 12 +++---------
 drivers/scsi/ufs/ufshcd.h |  6 ------
 2 files changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 3912b74d50ae..64ac9e48c4d7 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1192,12 +1192,9 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
 	return ret;
 }
 
-static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
+static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
 {
-	if (writelock)
-		ufshcd_up_write(hba);
-	else
-		ufshcd_up_read(hba);
+	ufshcd_up_write(hba);
 	ufshcd_scsi_unblock_requests(hba);
 	ufshcd_release(hba);
 }
@@ -1214,7 +1211,6 @@ static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
 static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
 {
 	int ret = 0;
-	bool is_writelock = true;
 
 	ret = ufshcd_clock_scaling_prepare(hba);
 	if (ret)
@@ -1244,12 +1240,10 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
 	}
 
 	/* Enable Write Booster if we have scaled up else disable it */
-	ufshcd_downgrade_write(hba);
-	is_writelock = false;
 	ufshcd_wb_toggle(hba, scale_up);
 
 out_unprepare:
-	ufshcd_clock_scaling_unprepare(hba, is_writelock);
+	ufshcd_clock_scaling_unprepare(hba);
 	return ret;
 }
 
diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index 74891947bb34..47f81eae178c 100644
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -1457,10 +1457,4 @@ static inline void ufshcd_up_write(struct ufs_hba *hba)
 	up_write(&hba->host_rw_sem);
 }
 
-static inline void ufshcd_downgrade_write(struct ufs_hba *hba)
-{
-	hba->excl_task = NULL;
-	downgrade_write(&hba->host_rw_sem);
-}
-
 #endif /* End of Header */
-- 
2.25.1