Re: [dpdk-dev] net/e1000: fix segfault on tx done clean up

["Zhao1, Wei" <wei.zhao1@intel.com>]

Reviewed-by: Wei Zhao <wei.zhao1@intel.com>

> -----Original Message-----
> From: Guo, Jia <jia.guo@intel.com>
> Sent: Thursday, July 16, 2020 4:54 PM
> To: Zhao1, Wei <wei.zhao1@intel.com>
> Cc: bmcfall@redhat.com; dev@dpdk.org; Guo, Jia <jia.guo@intel.com>
> Subject: [dpdk-dev] net/e1000: fix segfault on tx done clean up
> 
> As tx mbuf is not set for some advanced descriptors, if there is no mbuf
> checking before rte_pktmbuf_free_seg() function be called on the process of tx
> done clean up, that will cause a segfault. So add a NULL pointer check to fix it.
> 
> Bugzilla ID: 501
> Fixes: 8d907d2b79f7 (net/igb: free consumed Tx buffers on demand)
> 
> Signed-off-by: Jeff Guo <jia.guo@intel.com>
> ---
>  drivers/net/e1000/igb_rxtx.c | 170 +++++++++++++++++------------------
>  1 file changed, 82 insertions(+), 88 deletions(-)
> 
> diff --git a/drivers/net/e1000/igb_rxtx.c b/drivers/net/e1000/igb_rxtx.c index
> 5717cdb70..115a723e4 100644
> --- a/drivers/net/e1000/igb_rxtx.c
> +++ b/drivers/net/e1000/igb_rxtx.c
> @@ -1295,113 +1295,107 @@ igb_tx_done_cleanup(struct igb_tx_queue *txq,
> uint32_t free_cnt)
>  	uint16_t tx_id;    /* Current segment being processed. */
>  	uint16_t tx_last;  /* Last segment in the current packet. */
>  	uint16_t tx_next;  /* First segment of the next packet. */
> -	int count;
> +	int count = 0;
> 
> -	if (txq != NULL) {
> -		count = 0;
> -		sw_ring = txq->sw_ring;
> -		txr = txq->tx_ring;
> +	if (!txq)
> +		return = -ENODEV;
> 
> -		/*
> -		 * tx_tail is the last sent packet on the sw_ring. Goto the end
> -		 * of that packet (the last segment in the packet chain) and
> -		 * then the next segment will be the start of the oldest segment
> -		 * in the sw_ring. This is the first packet that will be
> -		 * attempted to be freed.
> -		 */
> +	sw_ring = txq->sw_ring;
> +	txr = txq->tx_ring;
> 
> -		/* Get last segment in most recently added packet. */
> -		tx_first = sw_ring[txq->tx_tail].last_id;
> +	/* tx_tail is the last sent packet on the sw_ring. Goto the end
> +	 * of that packet (the last segment in the packet chain) and
> +	 * then the next segment will be the start of the oldest segment
> +	 * in the sw_ring. This is the first packet that will be
> +	 * attempted to be freed.
> +	 */
> 
> -		/* Get the next segment, which is the oldest segment in ring. */
> -		tx_first = sw_ring[tx_first].next_id;
> +	/* Get last segment in most recently added packet. */
> +	tx_first = sw_ring[txq->tx_tail].last_id;
> 
> -		/* Set the current index to the first. */
> -		tx_id = tx_first;
> +	/* Get the next segment, which is the oldest segment in ring. */
> +	tx_first = sw_ring[tx_first].next_id;
> 
> -		/*
> -		 * Loop through each packet. For each packet, verify that an
> -		 * mbuf exists and that the last segment is free. If so, free
> -		 * it and move on.
> -		 */
> -		while (1) {
> -			tx_last = sw_ring[tx_id].last_id;
> -
> -			if (sw_ring[tx_last].mbuf) {
> -				if (txr[tx_last].wb.status &
> -						E1000_TXD_STAT_DD) {
> -					/*
> -					 * Increment the number of packets
> -					 * freed.
> -					 */
> -					count++;
> -
> -					/* Get the start of the next packet. */
> -					tx_next = sw_ring[tx_last].next_id;
> -
> -					/*
> -					 * Loop through all segments in a
> -					 * packet.
> -					 */
> -					do {
> -						rte_pktmbuf_free_seg(sw_ring[tx_id].mbuf);
> +	/* Set the current index to the first. */
> +	tx_id = tx_first;
> +
> +	/* Loop through each packet. For each packet, verify that an
> +	 * mbuf exists and that the last segment is free. If so, free
> +	 * it and move on.
> +	 */
> +	while (1) {
> +		tx_last = sw_ring[tx_id].last_id;
> +
> +		if (sw_ring[tx_last].mbuf) {
> +			if (txr[tx_last].wb.status &
> +			    E1000_TXD_STAT_DD) {
> +				/* Increment the number of packets
> +				 * freed.
> +				 */
> +				count++;
> +
> +				/* Get the start of the next packet. */
> +				tx_next = sw_ring[tx_last].next_id;
> +
> +				/* Loop through all segments in a
> +				 * packet.
> +				 */
> +				do {
> +					if (sw_ring[tx_id].mbuf) {
> +						rte_pktmbuf_free_seg(
> +							sw_ring[tx_id].mbuf);
>  						sw_ring[tx_id].mbuf = NULL;
>  						sw_ring[tx_id].last_id = tx_id;
> +					}
> 
> -						/* Move to next segemnt. */
> -						tx_id = sw_ring[tx_id].next_id;
> +					/* Move to next segemnt. */
> +					tx_id = sw_ring[tx_id].next_id;
> 
> -					} while (tx_id != tx_next);
> +				} while (tx_id != tx_next);
> 
> -					if (unlikely(count == (int)free_cnt))
> -						break;
> -				} else
> -					/*
> -					 * mbuf still in use, nothing left to
> -					 * free.
> -					 */
> +				if (unlikely(count == (int)free_cnt))
>  					break;
>  			} else {
> -				/*
> -				 * There are multiple reasons to be here:
> -				 * 1) All the packets on the ring have been
> -				 *    freed - tx_id is equal to tx_first
> -				 *    and some packets have been freed.
> -				 *    - Done, exit
> -				 * 2) Interfaces has not sent a rings worth of
> -				 *    packets yet, so the segment after tail is
> -				 *    still empty. Or a previous call to this
> -				 *    function freed some of the segments but
> -				 *    not all so there is a hole in the list.
> -				 *    Hopefully this is a rare case.
> -				 *    - Walk the list and find the next mbuf. If
> -				 *      there isn't one, then done.
> +				/* mbuf still in use, nothing left to
> +				 * free.
>  				 */
> -				if (likely((tx_id == tx_first) && (count != 0)))
> -					break;
> +				break;
> +			}
> +		} else {
> +			/* There are multiple reasons to be here:
> +			 * 1) All the packets on the ring have been
> +			 *    freed - tx_id is equal to tx_first
> +			 *    and some packets have been freed.
> +			 *    - Done, exit
> +			 * 2) Interfaces has not sent a rings worth of
> +			 *    packets yet, so the segment after tail is
> +			 *    still empty. Or a previous call to this
> +			 *    function freed some of the segments but
> +			 *    not all so there is a hole in the list.
> +			 *    Hopefully this is a rare case.
> +			 *    - Walk the list and find the next mbuf. If
> +			 *      there isn't one, then done.
> +			 */
> +			if (likely(tx_id == tx_first && count != 0))
> +				break;
> 
> -				/*
> -				 * Walk the list and find the next mbuf, if any.
> -				 */
> -				do {
> -					/* Move to next segemnt. */
> -					tx_id = sw_ring[tx_id].next_id;
> +			/* Walk the list and find the next mbuf, if any. */
> +			do {
> +				/* Move to next segemnt. */
> +				tx_id = sw_ring[tx_id].next_id;
> 
> -					if (sw_ring[tx_id].mbuf)
> -						break;
> +				if (sw_ring[tx_id].mbuf)
> +					break;
> 
> -				} while (tx_id != tx_first);
> +			} while (tx_id != tx_first);
> 
> -				/*
> -				 * Determine why previous loop bailed. If there
> -				 * is not an mbuf, done.
> -				 */
> -				if (sw_ring[tx_id].mbuf == NULL)
> -					break;
> -			}
> +			/* Determine why previous loop bailed. If there
> +			 * is not an mbuf, done.
> +			 */
> +			if (!sw_ring[tx_id].mbuf)
> +				break;
>  		}
> -	} else
> -		count = -ENODEV;
> +	}
> 
>  	return count;
>  }
> --
> 2.20.1