[PATCH] ufs: core: Fix a deadlock in the frequency scaling code

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

Commit 08b12cda6c44 ("scsi: ufs: core: Switch to scsi_get_internal_cmd()")
accidentally introduced a deadlock in the frequency scaling code.
ufshcd_clock_scaling_unprepare() may submit a device management command
while SCSI command processing is blocked. The deadlock was introduced by
using the SCSI core for submitting device management commands
(scsi_get_internal_cmd() + blk_execute_rq()). Fix this deadlock by calling
blk_mq_unquiesce_tagset() before any device management commands are
submitted by ufshcd_clock_scaling_unprepare().

Fixes: 08b12cda6c44 ("scsi: ufs: core: Switch to scsi_get_internal_cmd()")
Reported-by: Manivannan Sadhasivam <mani@kernel.org>
Reported-by: Roger Shimizu <rosh@debian.org>
Closes: https://lore.kernel.org/linux-scsi/ehorjaflathzab5oekx2nae2zss5vi2r36yqkqsfjb2fgsifz2@yk3us5g3igow/
Tested-by: Roger Shimizu <rosh@debian.org>
Cc: Nitin Rawat <nitin.rawat@oss.qualcomm.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/ufs/core/ufshcd.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 1837ae204d5e..80c0b49f30b0 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -1455,15 +1455,14 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba, u64 timeout_us)
 static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, int err)
 {
 	up_write(&hba->clk_scaling_lock);
+	mutex_unlock(&hba->wb_mutex);
+	blk_mq_unquiesce_tagset(&hba->host->tag_set);
+	mutex_unlock(&hba->host->scan_mutex);
 
 	/* Enable Write Booster if current gear requires it else disable it */
 	if (ufshcd_enable_wb_if_scaling_up(hba) && !err)
 		ufshcd_wb_toggle(hba, hba->pwr_info.gear_rx >= hba->clk_scaling.wb_gear);
 
-	mutex_unlock(&hba->wb_mutex);
-
-	blk_mq_unquiesce_tagset(&hba->host->tag_set);
-	mutex_unlock(&hba->host->scan_mutex);
 	ufshcd_release(hba);
 }