scsi: ufs: fix deadlock between clock scaling and clock ungating work

There's a deadlock between clock scaling and clock ungating work if hibern8
exit fails while ungating clocks.

ufshcd_exec_dev_cmd() in clock ungating work blocks at taking
"clk_scaling_lock" unless clock scaling work completes which had taken
"clock_scaling_lock" and it will never be released hence this is a
deadlock.

Clock ungating context:
----------------------
-000|__switch_to()
-001|context_switch(inline)
-001|__schedule()
-002|schedule()
-003|rwsem_down_read_failed()
-004|down_read()
-005|ufshcd_get_dev_cmd_tag(inline)
-005|ufshcd_exec_dev_cmd()
-006|ufshcd_verify_dev_init()
-007|ufshcd_probe_hba()
-008|ufshcd_host_reset_and_restore()
-009|ufshcd_link_recovery()
-010|ufshcd_uic_hibern8_exit()
-011|ufshcd_ungate_work()
-012|static_key_count(inline)
-012|static_key_false(inline)
-012|trace_workqueue_execute_end(inline)
-012|process_one_work()
-013|process_scheduled_works(inline)
-013|worker_thread()
-014|kthread()
-015|ret_from_fork(asm)
 -->|exception
-016|NSX:0xF0440E59300(asm)
 ---|end of frame

Clock scaling context:
----------------------
-000|__switch_to()
-001|context_switch(inline)
-001|__schedule()
-002|schedule()
-003|schedule_timeout()
-004|do_wait_for_common(inline)
-004|__wait_for_common(inline)
-004|wait_for_common()
-005|wait_for_completion()
-006|flush_work()
-007|ufshcd_hold()
-008|ufshcd_hold_all()
-009|ufshcd_wait_for_doorbell_clr()
-010|ufshcd_clock_scaling_prepare(inline)
-010|ufshcd_devfreq_scale()
-011|ufshcd_devfreq_target()
-012|update_devfreq()
-013|devfreq_monitor()
-014|static_key_count(inline)
-014|static_key_false(inline)
-014|trace_workqueue_execute_end(inline)
-014|process_one_work()
-015|worker_thread()
-016|kthread()
-017|ret_from_fork(asm)
 -->|exception
-018|NSR:0x2A714C(asm)
---|end of frame

This change is fixing this by moving ufshcd_hold_all() in
ufshcd_devfreq_scale() to the beginning of the function so that
clk_scaling_lock is acquired only after clock ungating completes.

CRs-Fixed: 963407
Change-Id: I83788c3212baeab31cf1bf877ca0aaf9005ca661
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>

1 files changed, 9 insertions, 7 deletions

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 740509c34b0a..b2a16e465246 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -8589,17 +8589,18 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
 {
 	int ret = 0;
 
+	/* let's not get into low power until clock scaling is completed */
+	ufshcd_hold_all(hba);
+
 	ret = ufshcd_clock_scaling_prepare(hba);
 	if (ret)
-		return ret;
+		goto out;
 
-	/* let's not get into low power until clock scaling is completed */
-	ufshcd_hold_all(hba);
 	/* scale down the gear before scaling down clocks */
 	if (!scale_up) {
 		ret = ufshcd_scale_gear(hba, false);
 		if (ret)
-			goto out;
+			goto clk_scaling_unprepare;
 	}
 
 	ret = ufshcd_scale_clks(hba, scale_up);
@@ -8611,7 +8612,7 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
 		ret = ufshcd_scale_gear(hba, true);
 		if (ret) {
 			ufshcd_scale_clks(hba, false);
-			goto out;
+			goto clk_scaling_unprepare;
 		}
 	}
 
@@ -8625,13 +8626,14 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
 				hba->clk_gating.delay_ms_pwr_save;
 	}
 
-	goto out;
+	goto clk_scaling_unprepare;
 
 scale_up_gear:
 	if (!scale_up)
 		ufshcd_scale_gear(hba, true);
-out:
+clk_scaling_unprepare:
 	ufshcd_clock_scaling_unprepare(hba);
+out:
 	ufshcd_release_all(hba);
 	return ret;
 }