Re: [PATCH 15/15] net/dpaa: fix buffer free in slow path

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 10/6/2022 9:51 AM, Gagandeep Singh wrote:
> Hi,
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@amd.com>
>> Sent: Wednesday, October 5, 2022 7:52 PM
>> To: Gagandeep Singh <G.Singh@nxp.com>; dev@dpdk.org
>> Cc: stable@dpdk.org
>> Subject: Re: [PATCH 15/15] net/dpaa: fix buffer free in slow path
>>
>> On 9/28/2022 6:25 AM, Gagandeep Singh wrote:
>>> Adding a check in slow path to free those buffers which are not
>>> external.
>>>
>>
>> Can you please explain what was the error before fix, what was happening
>> when you try to free all mbufs?
>>
>> Also it seems previous logic was different, with 'prev_seg' etc, can you
>> explain what/why changed there?
>>
> Actually, there were two issues, this function was converting all the segments present in HW frame
> descriptor to mbuf SG list by doing while on segments in FD (HW descriptor) and in the end
> it frees only one segment by calling the API rte_pktmbuf_free_seg(), so for other segments
> memory will be leaked.
> 

ack

> Now in this change, doing the loop on each segment in FD and if the segment has a valid
> buffer pool id (HW pool id), freeing that segment in the loop itself without converting to a mbuf list.
> if we free all the buffers even those with invalid HW bpid (which will only be the external buffer case),
> then there can be double free because all the external buffer free handling is being done by the
> Xmit function.
> 

Got it, can you please give more information in the commit log as above, 
and can you please elaborate impact of possible double free, will it 
crash etc?

>>> Fixes: 9124e65dd3eb ("net/dpaa: enable Tx queue taildrop")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Gagandeep Singh <g.singh@nxp.com>
>>> ---
>>>    drivers/net/dpaa/dpaa_rxtx.c | 23 ++++++++---------------
>>>    1 file changed, 8 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/drivers/net/dpaa/dpaa_rxtx.c
>>> b/drivers/net/dpaa/dpaa_rxtx.c index 4d285b4f38..ce4f3d6c85 100644
>>> --- a/drivers/net/dpaa/dpaa_rxtx.c
>>> +++ b/drivers/net/dpaa/dpaa_rxtx.c
>>> @@ -455,7 +455,7 @@ dpaa_free_mbuf(const struct qm_fd *fd)
>>>    	bp_info = DPAA_BPID_TO_POOL_INFO(fd->bpid);
>>>    	format = (fd->opaque & DPAA_FD_FORMAT_MASK) >>
>> DPAA_FD_FORMAT_SHIFT;
>>>    	if (unlikely(format == qm_fd_sg)) {
>>> -		struct rte_mbuf *first_seg, *prev_seg, *cur_seg, *temp;
>>> +		struct rte_mbuf *first_seg, *cur_seg;
>>>    		struct qm_sg_entry *sgt, *sg_temp;
>>>    		void *vaddr, *sg_vaddr;
>>>    		int i = 0;
>>> @@ -469,32 +469,25 @@ dpaa_free_mbuf(const struct qm_fd *fd)
>>>    		sgt = vaddr + fd_offset;
>>>    		sg_temp = &sgt[i++];
>>>    		hw_sg_to_cpu(sg_temp);
>>> -		temp = (struct rte_mbuf *)
>>> -			((char *)vaddr - bp_info->meta_data_size);
>>>    		sg_vaddr = DPAA_MEMPOOL_PTOV(bp_info,
>>>
>> 	qm_sg_entry_get64(sg_temp));
>>> -
>>>    		first_seg = (struct rte_mbuf *)((char *)sg_vaddr -
>>>    						bp_info->meta_data_size);
>>>    		first_seg->nb_segs = 1;
>>> -		prev_seg = first_seg;
>>>    		while (i < DPAA_SGT_MAX_ENTRIES) {
>>>    			sg_temp = &sgt[i++];
>>>    			hw_sg_to_cpu(sg_temp);
>>> -			sg_vaddr = DPAA_MEMPOOL_PTOV(bp_info,
>>> +			if (sg_temp->bpid != 0xFF) {
>>> +				bp_info =
>> DPAA_BPID_TO_POOL_INFO(sg_temp->bpid);
>>> +				sg_vaddr = DPAA_MEMPOOL_PTOV(bp_info,
>>>
>> 	qm_sg_entry_get64(sg_temp));
>>> -			cur_seg = (struct rte_mbuf *)((char *)sg_vaddr -
>>> +				cur_seg = (struct rte_mbuf *)((char
>> *)sg_vaddr -
>>>    						      bp_info-
>>> meta_data_size);
>>> -			first_seg->nb_segs += 1;
>>> -			prev_seg->next = cur_seg;
>>> -			if (sg_temp->final) {
>>> -				cur_seg->next = NULL;
>>> -				break;
>>> +				rte_pktmbuf_free_seg(cur_seg);
>>>    			}
>>> -			prev_seg = cur_seg;
>>> +			if (sg_temp->final)
>>> +				break;
>>>    		}
>>> -
>>> -		rte_pktmbuf_free_seg(temp);
>>>    		rte_pktmbuf_free_seg(first_seg);
>>>    		return 0;
>>>    	}
>