linux-kernel - Re: [PATCH v4 4/4] bus: mhi: host: Take irqsave lock after TRE is generated

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Message-ID: <ae1514d1-1cdf-42f8-ac8c-6e6c2005922f@quicinc.com>
Date:   Mon, 27 Nov 2023 15:19:49 +0800
From:   Qiang Yu <quic_qianyu@...cinc.com>
To:     Manivannan Sadhasivam <mani@...nel.org>
CC:     <quic_jhugo@...cinc.com>, <mhi@...ts.linux.dev>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_cang@...cinc.com>, <quic_mrana@...cinc.com>,
        Hemant Kumar <quic_hemantk@...cinc.com>,
        Lazarus Motha <quic_lmotha@...cinc.com>
Subject: Re: [PATCH v4 4/4] bus: mhi: host: Take irqsave lock after TRE is
 generated


On 11/24/2023 6:09 PM, Manivannan Sadhasivam wrote:
> On Tue, Nov 14, 2023 at 01:27:41PM +0800, Qiang Yu wrote:
>> From: Hemant Kumar <quic_hemantk@...cinc.com>
>>
>> If CONFIG_TRACE_IRQFLAGS is enabled, irq will be enabled once __local_bh_
>> enable_ip is called as part of write_unlock_bh. Hence, let's take irqsave
> "__local_bh_enable_ip" is a function name, so you should not break it.
Thanks for let me know, will note this in following patch.
>
>> lock after TRE is generated to avoid running write_unlock_bh when irqsave
>> lock is held.
>>
> I still don't understand this commit message. Where is the write_unlock_bh()
> being called?
>
> - Mani
Write_unlock_bh() is invoked in mhi_gen_te()
The calling flow is like
mhi_queue
     read_lock_irqsave(&mhi_cntrl->pm_lock, flags)
     mhi_gen_tre
         write_lock_bh(&mhi_chan->lock)
         write_unlock_bh(&mhi_chan->lock)   // Will enable irq if 
CONFIG_TRACE_IRQFLAGS is enabled
     read_lock_irqsave(&mhi_cntrl->pm_lock, flags)

after adding this patch, the calling flow becomes

mhi_queue
     mhi_gen_tre
         write_lock_bh(&mhi_chan->lock)
         write_unlock_bh(&mhi_chan->lock)
     read_lock_irqsave(&mhi_cntrl->pm_lock, flags)
     read_lock_irqsave(&mhi_cntrl->pm_lock, flags)
>
>> Signed-off-by: Hemant Kumar <quic_hemantk@...cinc.com>
>> Signed-off-by: Lazarus Motha <quic_lmotha@...cinc.com>
>> Signed-off-by: Qiang Yu <quic_qianyu@...cinc.com>
>> ---
>>   drivers/bus/mhi/host/main.c | 13 +++++--------
>>   1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
>> index 33f27e2..d7abd0b 100644
>> --- a/drivers/bus/mhi/host/main.c
>> +++ b/drivers/bus/mhi/host/main.c
>> @@ -1128,17 +1128,15 @@ static int mhi_queue(struct mhi_device *mhi_dev, struct mhi_buf_info *buf_info,
>>   	if (unlikely(MHI_PM_IN_ERROR_STATE(mhi_cntrl->pm_state)))
>>   		return -EIO;
>>   
>> -	read_lock_irqsave(&mhi_cntrl->pm_lock, flags);
>> -
>>   	ret = mhi_is_ring_full(mhi_cntrl, tre_ring);
>> -	if (unlikely(ret)) {
>> -		ret = -EAGAIN;
>> -		goto exit_unlock;
>> -	}
>> +	if (unlikely(ret))
>> +		return -EAGAIN;
>>   
>>   	ret = mhi_gen_tre(mhi_cntrl, mhi_chan, buf_info, mflags);
>>   	if (unlikely(ret))
>> -		goto exit_unlock;
>> +		return ret;
>> +
>> +	read_lock_irqsave(&mhi_cntrl->pm_lock, flags);
>>   
>>   	/* Packet is queued, take a usage ref to exit M3 if necessary
>>   	 * for host->device buffer, balanced put is done on buffer completion
>> @@ -1158,7 +1156,6 @@ static int mhi_queue(struct mhi_device *mhi_dev, struct mhi_buf_info *buf_info,
>>   	if (dir == DMA_FROM_DEVICE)
>>   		mhi_cntrl->runtime_put(mhi_cntrl);
>>   
>> -exit_unlock:
>>   	read_unlock_irqrestore(&mhi_cntrl->pm_lock, flags);
>>   
>>   	return ret;
>> -- 
>> 2.7.4
>>
>>