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Subject[PATCH 4.4 74/86] scsi: ufshcd: Fix race between clk scaling and ungate work
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Venkat Gopalakrishnan <venkatg@codeaurora.org>

commit f2a785ac23125fa0774327d39e837e45cf28fe92 upstream.

The ungate work turns on the clock before it exits hibern8, if the link
was put in hibern8 during clock gating work. There occurs a race
condition when clock scaling work calls ufshcd_hold() to make sure low
power states cannot be entered, but that returns by checking only
whether the clocks are on. This causes the clock scaling work to issue
UIC commands when the link is in hibern8 causing failures. Make sure we
exit hibern8 state before returning from ufshcd_hold().

Callstacks for race condition:

ufshcd_scale_gear
ufshcd_devfreq_scale
ufshcd_devfreq_target
update_devfreq
devfreq_monitor
process_one_work
worker_thread
kthread
ret_from_fork

ufshcd_uic_hibern8_exit
ufshcd_ungate_work
process_one_work
worker_thread
kthread
ret_from_fork

Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/scsi/ufs/ufshcd.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -585,6 +585,21 @@ int ufshcd_hold(struct ufs_hba *hba, boo
start:
switch (hba->clk_gating.state) {
case CLKS_ON:
+ /*
+ * Wait for the ungate work to complete if in progress.
+ * Though the clocks may be in ON state, the link could
+ * still be in hibner8 state if hibern8 is allowed
+ * during clock gating.
+ * Make sure we exit hibern8 state also in addition to
+ * clocks being ON.
+ */
+ if (ufshcd_can_hibern8_during_gating(hba) &&
+ ufshcd_is_link_hibern8(hba)) {
+ spin_unlock_irqrestore(hba->host->host_lock, flags);
+ flush_work(&hba->clk_gating.ungate_work);
+ spin_lock_irqsave(hba->host->host_lock, flags);
+ goto start;
+ }
break;
case REQ_CLKS_OFF:
if (cancel_delayed_work(&hba->clk_gating.gate_work)) {

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