Re: [PATCH v2 1/2] bus: mhi: host: Add spinlock to protect WP access when queueing TREs

[Qiang Yu <quic_qianyu@quicinc.com>]

On 11/6/2023 12:41 PM, Manivannan Sadhasivam wrote:
> On Wed, Sep 13, 2023 at 04:47:40PM +0800, Qiang Yu wrote:
>> From: Bhaumik Bhatt <bbhatt@codeaurora.org>
>>
>> Protect WP accesses such that multiple threads queueing buffers for
>> incoming data do not race and access the same WP twice. Ensure read and
>> write locks for the channel are not taken in succession by dropping the
>> read lock from parse_xfer_event() such that a callback given to client
>> can potentially queue buffers and acquire the write lock in that process.
>> Any queueing of buffers should be done without channel read lock acquired
>> as it can result in multiple locks and a soft lockup.
>>
> This change is doing two things:
>
> 1. Unlocking xfer_cb to prevent potential lockup
> 2. Protecting mhi_gen_tre() against concurrent access
>
> So you should split this into two patches and also add Fixes tag if appropriate.
>
> - Mani
Hi Mani, thanks for review. I split this into two patch and add Fixes tag.
>
>> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
>> Signed-off-by: Qiang Yu <quic_qianyu@quicinc.com>
>> ---
>>   drivers/bus/mhi/host/main.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
>> index dcf627b..13c4b89 100644
>> --- a/drivers/bus/mhi/host/main.c
>> +++ b/drivers/bus/mhi/host/main.c
>> @@ -642,6 +642,7 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
>>   			mhi_del_ring_element(mhi_cntrl, tre_ring);
>>   			local_rp = tre_ring->rp;
>>   
>> +			read_unlock_bh(&mhi_chan->lock);
>>   			/* notify client */
>>   			mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
>>   
>> @@ -667,6 +668,7 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
>>   					kfree(buf_info->cb_buf);
>>   				}
>>   			}
>> +			read_lock_bh(&mhi_chan->lock);
>>   		}
>>   		break;
>>   	} /* CC_EOT */
>> @@ -1204,6 +1206,9 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
>>   	int eot, eob, chain, bei;
>>   	int ret;
>>   
>> +	/* Protect accesses for reading and incrementing WP */
>> +	write_lock_bh(&mhi_chan->lock);
>> +
>>   	buf_ring = &mhi_chan->buf_ring;
>>   	tre_ring = &mhi_chan->tre_ring;
>>   
>> @@ -1221,8 +1226,10 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
>>   
>>   	if (!info->pre_mapped) {
>>   		ret = mhi_cntrl->map_single(mhi_cntrl, buf_info);
>> -		if (ret)
>> +		if (ret) {
>> +			write_unlock_bh(&mhi_chan->lock);
>>   			return ret;
>> +		}
>>   	}
>>   
>>   	eob = !!(flags & MHI_EOB);
>> @@ -1239,6 +1246,8 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
>>   	mhi_add_ring_element(mhi_cntrl, tre_ring);
>>   	mhi_add_ring_element(mhi_cntrl, buf_ring);
>>   
>> +	write_unlock_bh(&mhi_chan->lock);
>> +
>>   	return 0;
>>   }
>>   
>> -- 
>> 2.7.4
>>
>>