---
- branch: MAIN
  date: Sat Jan 29 21:37:07 UTC 2022
  files:
  - new: '1.44'
    old: '1.43'
    path: src/sys/dev/usb/usbnet.c
    pathrev: src/sys/dev/usb/usbnet.c@1.44
    type: modified
  id: 20220129T213707Z.b957c16d73f90f9bf2c3854f6ce4407427e22a33
  log: |
    usbnet: Defer hardware multicast filter updates to USB task.

    Breaks deadlock:

    - usbnet_detach holds usbnet lock, awaits kpause in ure_reset
    - callout holds softclock `lock' (sequential softints, blocks kpause
      wakeup), awaits softnet_lock in tcp_timer_keep, frag6_fasttimo, &c.
    - soclose holds softnet_lock, awaits usbnet lock in SIOCDELMULTI

    This change breaks the deadlock by not passing the SIOCADDMULTI or
    SIOCDELMULTI ioctl synchronously to the driver, which typically takes
    the usbnet lock.

    With this change, the ethernet layer still maintains the list of
    multicast addresses synchronously, but we defer the driver logic that
    updates the hardware multicast filter to an asynchronous USB task
    without softnet_lock held.

    This doesn't cause exactly the same ioctl to be sent to the driver --
    usbnet just sends SIOCDELMULTI with an all-zero struct ifreq, and
    might drop some ioctls if issued in quick succession.  This is OK
    because none of the drivers actually distinguish between SIOCADDMULTI
    and SIOCDELMULTI, or examine the argument; the drivers just commit
    whatever multicast addresses are listed in the ethercom.

    Other than the different ioctl submitted, there is no change to the
    ABI or locking scheme of usbnet, so this is safe to pull up to
    netbsd-9.  This means we unfortunately can't guarantee that if a
    process issues SIOCADDMULTI and then sendto, the multicast filter
    update will be done by the time of the sendto -- and, more
    importantly, the packets received in reply to it.  But failing to
    guarantee that is better than deadlocking!  Later changes on HEAD
    will restore the synchronous multicast filter updates with much more
    extensive ABI changes and API simplifications in usbnet(9).

    Proposed on tech-net:
    https://mail-index.netbsd.org/tech-net/2021/12/30/msg008164.html

    XXX pullup-9
  module: src
  subject: 'CVS commit: src/sys/dev/usb'
  unixtime: '1643492227'
  user: riastradh