Re: [PATCH v3] ufs: core: fix lockdep warning of clk_scaling_lock

[Peter Wang <peter.wang@mediatek.com>]

On 7/26/22 11:05 PM, Greg KH wrote:
> On Tue, Jul 26, 2022 at 05:14:33PM +0800, peter.wang@mediatek.com wrote:
>> From: Peter Wang <peter.wang@mediatek.com>
>>
>> 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.
>>
>> ufshcd_wb_toggle can protected by hba->clk_scaling.is_allowed to make sure
>> ufshcd_devfreq_scale function not run concurrently.
>>
>> Fixes: 0e9d4ca43ba8 ("scsi: ufs: Protect some contexts from unexpected clock scaling")
>> Signed-off-by: Peter Wang <peter.wang@mediatek.com>
>> ---
>>   drivers/ufs/core/ufshcd.c | 27 ++++++++++++++++-----------
>>   1 file changed, 16 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
>> index c7b337480e3e..aa57126fdb49 100644
>> --- a/drivers/ufs/core/ufshcd.c
>> +++ b/drivers/ufs/core/ufshcd.c
>> @@ -272,6 +272,7 @@ static void ufshcd_wb_toggle_flush_during_h8(struct ufs_hba *hba, bool set);
>>   static inline void ufshcd_wb_toggle_flush(struct ufs_hba *hba, bool enable);
>>   static void ufshcd_hba_vreg_set_lpm(struct ufs_hba *hba);
>>   static void ufshcd_hba_vreg_set_hpm(struct ufs_hba *hba);
>> +static void ufshcd_clk_scaling_allow(struct ufs_hba *hba, bool allow);
>>   
>>   static inline void ufshcd_enable_irq(struct ufs_hba *hba)
>>   {
>> @@ -1249,12 +1250,10 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
>>   	return ret;
>>   }
>>   
>> -static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
>> +static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
>>   {
>> -	if (writelock)
>> -		up_write(&hba->clk_scaling_lock);
>> -	else
>> -		up_read(&hba->clk_scaling_lock);
>> +	up_write(&hba->clk_scaling_lock);
>> +
>>   	ufshcd_scsi_unblock_requests(hba);
>>   	ufshcd_release(hba);
>>   }
>> @@ -1271,7 +1270,7 @@ static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
>>   static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
>>   {
>>   	int ret = 0;
>> -	bool is_writelock = true;
>> +	bool wb_toggle = false;
>>   
>>   	ret = ufshcd_clock_scaling_prepare(hba);
>>   	if (ret)
>> @@ -1300,13 +1299,19 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
>>   		}
>>   	}
>>   
>> -	/* Enable Write Booster if we have scaled up else disable it */
>> -	downgrade_write(&hba->clk_scaling_lock);
>> -	is_writelock = false;
>> -	ufshcd_wb_toggle(hba, scale_up);
>> +	/* Disable clk_scaling until ufshcd_wb_toggle finish */
>> +	hba->clk_scaling.is_allowed = false;
>> +	wb_toggle = true;
>>   
>>   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);
>> +		ufshcd_clk_scaling_allow(hba, true);
>> +	}
>> +
>>   	return ret;
>>   }
>>   
>> -- 
>> 2.18.0
>>
> <formletter>
>
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>      https://urldefense.com/v3/__https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html__;!!CTRNKA9wMg0ARbw!24V8xNPFu0-WdpS3FH6jpUbnVGjhGphz8M0EYnzuRQWgnNx5qPBSLSwEtdHFyz63fw$
> for how to do this properly.

Hi Greg,


Thank you for remind.

Will use correct way next version


Thanks

Peter



>
> </formletter>