Patch "igc: Fix inserting of empty frame for launchtime" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    igc: Fix inserting of empty frame for launchtime

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     igc-fix-inserting-of-empty-frame-for-launchtime.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 28e19afbca0fa1e531bf500dfb1772f86514af4d
Author: Florian Kauer <florian.kauer@xxxxxxxxxxxxx>
Date:   Wed Jun 14 16:07:14 2023 +0200

    igc: Fix inserting of empty frame for launchtime
    
    [ Upstream commit 0bcc62858d6ba62cbade957d69745e6adeed5f3d ]
    
    The insertion of an empty frame was introduced with
    commit db0b124f02ba ("igc: Enhance Qbv scheduling by using first flag bit")
    in order to ensure that the current cycle has at least one packet if
    there is some packet to be scheduled for the next cycle.
    
    However, the current implementation does not properly check if
    a packet is already scheduled for the current cycle. Currently,
    an empty packet is always inserted if and only if
    txtime >= end_of_cycle && txtime > last_tx_cycle
    but since last_tx_cycle is always either the end of the current
    cycle (end_of_cycle) or the end of a previous cycle, the
    second part (txtime > last_tx_cycle) is always true unless
    txtime == last_tx_cycle.
    
    What actually needs to be checked here is if the last_tx_cycle
    was already written within the current cycle, so an empty frame
    should only be inserted if and only if
    txtime >= end_of_cycle && end_of_cycle > last_tx_cycle.
    
    This patch does not only avoid an unnecessary insertion, but it
    can actually be harmful to insert an empty packet if packets
    are already scheduled in the current cycle, because it can lead
    to a situation where the empty packet is actually processed
    as the first packet in the upcoming cycle shifting the packet
    with the first_flag even one cycle into the future, finally leading
    to a TX hang.
    
    The TX hang can be reproduced on a i225 with:
    
        sudo tc qdisc replace dev enp1s0 parent root handle 100 taprio \
                num_tc 1 \
                map 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 \
                queues 1@0 \
                base-time 0 \
                sched-entry S 01 300000 \
                flags 0x1 \
                txtime-delay 500000 \
                clockid CLOCK_TAI
        sudo tc qdisc replace dev enp1s0 parent 100:1 etf \
                clockid CLOCK_TAI \
                delta 500000 \
                offload \
                skip_sock_check
    
    and traffic generator
    
        sudo trafgen -i traffic.cfg -o enp1s0 --cpp -n0 -q -t1400ns
    
    with traffic.cfg
    
        #define ETH_P_IP        0x0800
    
        {
          /* Ethernet Header */
          0x30, 0x1f, 0x9a, 0xd0, 0xf0, 0x0e,  # MAC Dest - adapt as needed
          0x24, 0x5e, 0xbe, 0x57, 0x2e, 0x36,  # MAC Src  - adapt as needed
          const16(ETH_P_IP),
    
          /* IPv4 Header */
          0b01000101, 0,   # IPv4 version, IHL, TOS
          const16(1028),   # IPv4 total length (UDP length + 20 bytes (IP header))
          const16(2),      # IPv4 ident
          0b01000000, 0,   # IPv4 flags, fragmentation off
          64,              # IPv4 TTL
          17,              # Protocol UDP
          csumip(14, 33),  # IPv4 checksum
    
          /* UDP Header */
          10,  0, 48, 1,   # IP Src - adapt as needed
          10,  0, 48, 10,  # IP Dest - adapt as needed
          const16(5555),   # UDP Src Port
          const16(6666),   # UDP Dest Port
          const16(1008),   # UDP length (UDP header 8 bytes + payload length)
          csumudp(14, 34), # UDP checksum
    
          /* Payload */
          fill('W', 1000),
        }
    
    and the observed message with that is for example
    
     igc 0000:01:00.0 enp1s0: Detected Tx Unit Hang
       Tx Queue             <0>
       TDH                  <32>
       TDT                  <3c>
       next_to_use          <3c>
       next_to_clean        <32>
     buffer_info[next_to_clean]
       time_stamp           <ffff26a8>
       next_to_watch        <00000000632a1828>
       jiffies              <ffff27f8>
       desc.status          <1048000>
    
    Fixes: db0b124f02ba ("igc: Enhance Qbv scheduling by using first flag bit")
    Signed-off-by: Florian Kauer <florian.kauer@xxxxxxxxxxxxx>
    Reviewed-by: Kurt Kanzenbach <kurt@xxxxxxxxxxxxx>
    Tested-by: Naama Meir <naamax.meir@xxxxxxxxxxxxxxx>
    Signed-off-by: Tony Nguyen <anthony.l.nguyen@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 051b1048eb41b..631ce793fb2ec 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -918,7 +918,7 @@ static __le32 igc_tx_launchtime(struct igc_ring *ring, ktime_t txtime,
 			*first_flag = true;
 			ring->last_ff_cycle = baset_est;
 
-			if (ktime_compare(txtime, ring->last_tx_cycle) > 0)
+			if (ktime_compare(end_of_cycle, ring->last_tx_cycle) > 0)
 				*insert_empty = true;
 		}
 	}



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