[PATCH 0/1][SRU X] UBUNTU: SAUCE: bnxt_en_bpo: Fix TX timeout during netpoll

[Nivedita Singhvi]

BugLink: http://bugs.launchpad.net/bugs/1814095


[Impact]

The bnxt_en_bpo driver experienced tx timeouts causing the system to experience
network stalls and fail to send data and heartbeat packets.

The following 25Gb Broadcom NIC error was seen on Xenial running the
4.4.0-141-generic kernel on an amd64 host seeing moderate-heavy network
traffic (just once):

* The bnxt_en_po driver froze on a "TX timed out" error and triggered the
  Netdev Watchdog timer under load.

* From kernel log:
  "NETDEV WATCHDOG: eno2d1 (bnxt_en_bpo): transmit queue 0 timed out"
  See attached kern.log excerpt file for full excerpt of error log.

* Release = Xenial
  Kernel = 4.4.0-141-generic #167
  eno2d1 = Product Name: Broadcom Adv. Dual 25Gb Ethernet

* This caused the driver to reset in order to recover:

  "bnxt_en_bpo 0000:19:00.1 eno2d1: TX timeout detected, starting reset task!"

  driver: bnxt_en_bpo
  version: 1.8.1
  source: ubuntu/bnxt/bnxt.c: bnxt_tx_timeout()

* The loss of connectivity and softirq stall caused other cascading failures
  on the system.

* The bnxt_en_po driver is the imported Broadcom driver pulled in to support
  newer Broadcom HW (specific boards) while the bnx_en module continues to
  support the older HW. The current Linux upstream driver does not compile
  easily with the 4.4 kernel (too many changes).

* This upstream and bnxt_en driver fix is a likely solution:
   "bnxt_en: Fix TX timeout during netpoll"
   commit: 73f21c653f930f438d53eed29b5e4c65c8a0f906

  This fix has not been applied to the bnxt_en_po driver version, but review of
  the code indicates that it is susceptible to the bug, and the fix would be
  reasonable.


[Test Case]

* Unfortunately, this is not easy to reproduce. Also, it is only seen on
  4.4 kernels with newer Broadcom NICs supported by the bnxt_en_bpo driver.


[Regression Potential]

* The patch is restricted to the bpo driver, with very constrained scope
  - just the newest Broadcom NICs being used by the Xenial 4.4 kernel (as
  opposed to the hwe 4.15 etc. kernels, which would have the in-tree fixed
  driver).

* The patch is very small and backport is fairly minimal and simple.

* The fix has been running on the in-tree driver in upstream mainline as well
  as the Ubuntu Linux in-tree driver, although the Broadcom driver has a lot of
  lower level code that is different, this piece is still the same.


Michael Chan (1):
  The current netpoll implementation in the bnxt_en driver has problems
    that may miss TX completion events.  bnxt_poll_work() in effect is
    only handling at most 1 TX packet before exiting.  In addition,
    there may be in flight TX completions that ->poll() may miss even
    after we fix bnxt_poll_work() to handle all visible TX completions.
    netpoll may not call ->poll() again and HW may not generate IRQ
    because the driver does not ARM the IRQ when the budget (0 for
    netpoll) is reached.

 ubuntu/bnxt/bnxt.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

-- 
2.17.1