Hi Bart,
On 7/26/22 12:56 AM, Bart Van Assche wrote:
On 7/24/22 21:30, peter.wang@xxxxxxxxxxxx wrote:
From: Peter Wang <peter.wang@xxxxxxxxxxxx>
There have a lockdep warning like below in current flow.
kworker/u16:0: Possible unsafe locking scenario:
kworker/u16:0: CPU0 CPU1
kworker/u16:0: ---- ----
kworker/u16:0: lock(&hba->clk_scaling_lock);
kworker/u16:0: lock(&hba->dev_cmd.lock);
kworker/u16:0: lock(&hba->clk_scaling_lock);
kworker/u16:0: lock(&hba->dev_cmd.lock);
kworker/u16:0:
Before this patch clk_scaling_lock was held in reader mode during the
ufshcd_wb_toggle() call.
With this patch applied clk_scaling_lock is not held while
ufshcd_wb_toggle() is called.
This is safe because ufshcd_wb_toggle will held clk_scaling_lock in
reader mode "again" in flow
ufshcd_wb_toggle -> __ufshcd_wb_toggle -> ufshcd_query_flag_retry ->
ufshcd_query_flag ->
ufshcd_exec_dev_cmd -> down_read(&hba->clk_scaling_lock);
The protect should enough and make sure clock is not change while
send command.
Since this is a bug fix, please add a Fixes: tag.
Will add Fixes: tag in next version.
out_unprepare:
- ufshcd_clock_scaling_unprepare(hba, is_writelock);
+ ufshcd_clock_scaling_unprepare(hba);
+
+ /* Enable Write Booster if we have scaled up else disable it */
+ if (wb_toggle)
+ ufshcd_wb_toggle(hba, scale_up);
+
return ret;
}
Can the above patch can have the following unwanted effect?
* ufshcd_devfreq_scale() calls ufshcd_clock_scaling_unprepare().
* Clock scaling to a lower frequency happens.
* ufshcd_wb_toggle() enables the write booster.
Shouldn't the above ufshcd_wb_toggle() call be surrounded by
down_read() and up_read() calls in addition to a check whether the
WriteBooster really should be enabled instead of using 'scale_up'?
Thanks,
Bart.
You means ufshcd_devfreq_scale may have racing in two thread, right?
Then yes, it may have this unwanted effect in this condition.
But ufshcd_wb_toggle should not hold clk_scaling_lock, or the deadlock
may happen.
I will change this patch to protect ufshcd_devfreq_scale racing and
ufshcd_wb_toggle in next version.
Thanks.
Peter
