Re: [PATCH 1/1] rpmsg: virtio_rpmsg_bus - prevent possible race condition

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many thanks for your analysis, very interesting.

please find below an extract of your trace with my analysis:

  stm32mp1_bulk_p-390     [001] .....   907.241226: rpmsg_send
  stm32mp1_bulk_p-390     [001] .....   907.241228: virtio_rpmsg_send <-rpmsg_send
  stm32mp1_bulk_p-390     [001] .....   907.241237: virtqueue_enable_cb
  stm32mp1_bulk_p-390     [001] .....   907.241239: virtqueue_enable_cb_prepare

At this point seems that no more TX-buffer

      kworker/0:4-67      [000] .....   907.242533: vring_interrupt
      kworker/0:4-67      [000] .....   907.242536: rpmsg_xmit_done

Here you receive  an interrupt indicating that TX buffer has been released by
the remote. that's the expected behavior.

  stm32mp1_bulk_p-390     [000] .....   984.054941: rpmsg_send
  stm32mp1_bulk_p-390     [000] .....   984.054943: virtio_rpmsg_send <-rpmsg_send
  stm32mp1_bulk_p-390     [000] .....   984.054956: virtqueue_enable_cb
  stm32mp1_bulk_p-390     [000] .....   984.054958: virtqueue_enable_cb_prepare
  stm32mp1_bulk_p-390     [000] .....   999.398667: virtqueue_disable_cb
  stm32mp1_bulk_p-390     [000] .....   999.414840: rpmsg_send
  stm32mp1_bulk_p-390     [000] .....   999.414843: virtio_rpmsg_send <-rpmsg_send
  stm32mp1_bulk_p-390     [000] .....   999.414855: virtqueue_enable_cb
  stm32mp1_bulk_p-390     [000] .....   999.414857: virtqueue_enable_cb_prepare

Here you have again no more TX buffer. From this point there is no more activity
neither in TX nor in RX until the timeout of 15 seconds.
If you have a look to rproc_vq_interrupt the last one occurs at 907.242533

As you have no more virtqueue interrupts call for both directions, the issue is
probably either in the Cortex-M firmware, which seems to be stalled, or due to a
disable of the IRQs in Linux.

afaict we can rule out a complete stall of the cortex-m firmware: if we change the rpmsg_send to a rpmsg_trysend/msleep loop, the trysend will succeed to get a buffer after a few iterations.

or due to a disable of the IRQs in Linux.

do you have some recommendations how we could trace this?

many thanks,

  stm32mp1_bulk_p-390     [000] .....  1014.758678: virtqueue_disable_cb
  stm32mp1_bulk_p-390     [000] .....  1014.774802: rpmsg_send
  stm32mp1_bulk_p-390     [000] .....  1014.774804: virtio_rpmsg_send <-rpmsg_send
  stm32mp1_bulk_p-390     [000] .....  1014.774815: virtqueue_enable_cb

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