linux-kernel - Re: [PATCH v2] bus: mhi: core: Check state before processing power

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Date:   Wed, 24 Feb 2021 08:14:53 -0700
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     hemantk@...eaurora.org, bbhatt@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] bus: mhi: core: Check state before processing
 power_down

On 2/24/2021 2:55 AM, Manivannan Sadhasivam wrote:
> On Wed, Feb 17, 2021 at 09:43:31AM -0700, Jeffrey Hugo wrote:
>> We cannot process a power_down if the power state is DISABLED.  There is
>> no valid mhi_ctxt in that case, so attepting to process the power_down
>> will likely result in a null pointer dereference.  If the power state is
>> DISABLED, there is nothing to do anyways, so just bail early.
>>
>> Signed-off-by: Jeffrey Hugo <jhugo@...eaurora.org>
>> ---
>>
>> v2: Fix subject and tweak the locking to avoid needless lock/unlock/relock
>>
>>   drivers/bus/mhi/core/pm.c | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
>> index 56ba3ab..47f6621 100644
>> --- a/drivers/bus/mhi/core/pm.c
>> +++ b/drivers/bus/mhi/core/pm.c
>> @@ -1144,6 +1144,7 @@ int mhi_async_power_up(struct mhi_controller *mhi_cntrl)
>>   		mhi_deinit_dev_ctxt(mhi_cntrl);
>>   
>>   error_dev_ctxt:
>> +	mhi_cntrl->pm_state = MHI_PM_DISABLE;
>>   	mutex_unlock(&mhi_cntrl->pm_mutex);
>>   
>>   	return ret;
>> @@ -1155,11 +1156,17 @@ void mhi_power_down(struct mhi_controller *mhi_cntrl, bool graceful)
>>   	enum mhi_pm_state cur_state, transition_state;
>>   	struct device *dev = &mhi_cntrl->mhi_dev->dev;
>>   
>> +	mutex_lock(&mhi_cntrl->pm_mutex);
>> +	cur_state = mhi_cntrl->pm_state;
> 
> As I said in my previous review, you should use pm_lock for reading the
> pm_state.

You also said on IRC that is a refactor of the entire driver, and not a 
blocker for this fix.  Based on that, I intrepreted your comments as 
nothing needed to be done regarding the locking, so I'm confused by this 
comment.

I'm not entirely sure what you want since I feel like you are giving 
conflicting direction, but I'm guessing you want the lock of the pm_lock 
to be moved up to just under the mutex lock then?

-- 
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.