memif thread race condition on memif.disconnect()

["Bly, Mike" <mbly@ciena.com>]

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Hello,

We have run into a timing issue between threads when using the memif interface type and need some guidance.

Our application has a DPDK based process operating (among other things) a memif server interface. The problem is exposed when this memif interface receives a memif.disconnect message from the remote client, while in the middle of an rte_eth_rx_burst() on this same memif interface. As the IRQ message handling is on its own thread as compared to the DPDK worker thread doing the rx_burst, this resulted in a crash. The backtraces for which have been shared below. How does one ensure there are guard rails in place to gracefully exit the rx-burst when a disconnect occurs? Or, how do we properly modify the code such that  we defer responding to the disconnect CB after the rx-burst operation has completed?

We are utilizing DPDK 21.11.2. I have diff'd dpdks-stable:22.11.3 in ./drivers/net/memif, but I do not see anything obvious that would address this. I did a similar diff for dpdk:23.07, but do not see anything obvious there either.

-Mike

(gdb) thread 1
[Switching to thread 1 (Thread 0x7f17e2813600 (LWP 470))]
#0  0x00007f17e374d225 in eth_memif_rx (queue=0x1189023b00, bufs=0x7f17e28100e8, nb_pkts=32) at ../git/drivers/net/memif/rte_eth_memif.c:338
338                     last_slot = __atomic_load_n(&ring->head, __ATOMIC_ACQUIRE);
(gdb) bt
#0  0x00007f17e374d225 in eth_memif_rx (queue=0x1189023b00, bufs=0x7f17e28100e8, nb_pkts=32) at ../git/drivers/net/memif/rte_eth_memif.c:338
#1  0x000000000047e6fb in rte_eth_rx_burst (nb_pkts=32, rx_pkts=0x7f17e28100e8, queue_id=0, port_id=<optimized out>) at /usr/include/rte_ethdev.h:5368
#2  pmd_main_loop () at ../git/swfw/api/src/swfwPmd.c:1086
#3  0x000000000047f309 in pmd_launch_one_lcore (dummy=<optimized out>) at ../git/my_process.c:1157
#4  0x00007f17f7070e7c in eal_thread_loop (arg=<optimized out>) at ../git/lib/eal/linux/eal_thread.c:146
#5  0x00007f17f4c3da72 in start_thread (arg=<optimized out>) at pthread_create.c:442
#6  0x00007f17f4cbf930 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
(gdb) l
333             ring_size = 1 << mq->log2_ring_size;
334             mask = ring_size - 1;
335
336             if (type == MEMIF_RING_C2S) {
337                     cur_slot = mq->last_head;
338                     last_slot = __atomic_load_n(&ring->head, __ATOMIC_ACQUIRE);
339             } else {
340                     cur_slot = mq->last_tail;
341                     last_slot = __atomic_load_n(&ring->tail, __ATOMIC_ACQUIRE);
342             }
(gdb) p ring->head
Cannot access memory at address 0x7f17d8e58006

(gdb) thread 19
[Switching to thread 19 (Thread 0x7f17f0804600 (LWP 468))]
#0  0x00007f17f4caf97b in __GI___close (fd=494) at ../sysdeps/unix/sysv/linux/close.c:27
27        return SYSCALL_CANCEL (close, fd);
(gdb) bt
#0  0x00007f17f4caf97b in __GI___close (fd=494) at ../sysdeps/unix/sysv/linux/close.c:27
#1  0x00007f17e374f01f in memif_free_regions (dev=dev@entry=0x7f17f727f000 <rte_eth_devices+99072>) at ../git/drivers/net/memif/rte_eth_memif.c:882
#2  0x00007f17e37475d0 in memif_disconnect (dev=0x7f17f727f000 <rte_eth_devices+99072>) at ../git/drivers/net/memif/memif_socket.c:623
#3  0x00007f17f7091bd2 in eal_intr_process_interrupts (nfds=<optimized out>, events=<optimized out>) at ../git/lib/eal/linux/eal_interrupts.c:1026
#4  eal_intr_handle_interrupts (totalfds=<optimized out>, pfd=20) at ../git/lib/eal/linux/eal_interrupts.c:1100
#5  eal_intr_thread_main (arg=<optimized out>) at ../git/lib/eal/linux/eal_interrupts.c:1172
#6  0x00007f17f4c3da72 in start_thread (arg=<optimized out>) at pthread_create.c:442
#7  0x00007f17f4cbf930 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81


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