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Subject[PATCH 4.9 77/92] scsi: ufs: fix race between clock gating and devfreq scaling work
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Subhash Jadavani <subhashj@codeaurora.org>

commit 30fc33f1ef475480dc5bea4fe1bda84b003b992c upstream.

UFS devfreq clock scaling work may require clocks to be ON if it need to
execute some UFS commands hence it may request for clock hold before
issuing the command. But if UFS clock gating work is already running in
parallel, ungate work would end up waiting for the clock gating work to
finish and as clock gating work would also wait for the clock scaling
work to finish, we would enter in deadlock state. Here is the call trace
during this deadlock state:

Workqueue: devfreq_wq devfreq_monitor
__switch_to
__schedule
schedule
schedule_timeout
wait_for_common
wait_for_completion
flush_work
ufshcd_hold
ufshcd_send_uic_cmd
ufshcd_dme_get_attr
ufs_qcom_set_dme_vs_core_clk_ctrl_clear_div
ufs_qcom_clk_scale_notify
ufshcd_scale_clks
ufshcd_devfreq_target
update_devfreq
devfreq_monitor
process_one_work
worker_thread
kthread
ret_from_fork

Workqueue: events ufshcd_gate_work
__switch_to
__schedule
schedule
schedule_preempt_disabled
__mutex_lock_slowpath
mutex_lock
devfreq_monitor_suspend
devfreq_simple_ondemand_handler
devfreq_suspend_device
ufshcd_gate_work
process_one_work
worker_thread
kthread
ret_from_fork

Workqueue: events ufshcd_ungate_work
__switch_to
__schedule
schedule
schedule_timeout
wait_for_common
wait_for_completion
flush_work
__cancel_work_timer
cancel_delayed_work_sync
ufshcd_ungate_work
process_one_work
worker_thread
kthread
ret_from_fork

This change fixes this deadlock by doing this in devfreq work (devfreq_wq):
Try cancelling clock gating work. If we are able to cancel gating work
or it wasn't scheduled, hold the clock reference count until scaling is
in progress. If gate work is already running in parallel, let's skip
the frequecy scaling at this time and it will be retried once next scaling
window expires.

Reviewed-by: Sahitya Tummala <stummala@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 | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)

--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -6633,15 +6633,47 @@ static int ufshcd_devfreq_target(struct
{
int err = 0;
struct ufs_hba *hba = dev_get_drvdata(dev);
+ bool release_clk_hold = false;
+ unsigned long irq_flags;

if (!ufshcd_is_clkscaling_enabled(hba))
return -EINVAL;

+ spin_lock_irqsave(hba->host->host_lock, irq_flags);
+ if (ufshcd_eh_in_progress(hba)) {
+ spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
+ return 0;
+ }
+
+ if (ufshcd_is_clkgating_allowed(hba) &&
+ (hba->clk_gating.state != CLKS_ON)) {
+ if (cancel_delayed_work(&hba->clk_gating.gate_work)) {
+ /* hold the vote until the scaling work is completed */
+ hba->clk_gating.active_reqs++;
+ release_clk_hold = true;
+ hba->clk_gating.state = CLKS_ON;
+ } else {
+ /*
+ * Clock gating work seems to be running in parallel
+ * hence skip scaling work to avoid deadlock between
+ * current scaling work and gating work.
+ */
+ spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
+ return 0;
+ }
+ }
+ spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
+
if (*freq == UINT_MAX)
err = ufshcd_scale_clks(hba, true);
else if (*freq == 0)
err = ufshcd_scale_clks(hba, false);

+ spin_lock_irqsave(hba->host->host_lock, irq_flags);
+ if (release_clk_hold)
+ __ufshcd_release(hba);
+ spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
+
return err;
}


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