[PATCH v5 REPOST 0/6] fix hw_random stuck

[Amos Kong <akong@redhat.com>]

When I hotunplug a busy virtio-rng device or try to access
hwrng attributes in non-smp guest, it gets stuck.

My hotplug tests:

| test 0:
|   hotunplug rng device from qemu monitor
|
| test 1:
|   guest) # dd if=/dev/hwrng of=/dev/null &
|   hotunplug rng device from qemu monitor
|
| test 2:
|   guest) # dd if=/dev/random of=/dev/null &
|   hotunplug rng device from qemu monitor
|
| test 4:
|   guest) # dd if=/dev/hwrng of=/dev/null &
|   cat /sys/devices/virtual/misc/hw_random/rng_*
|
| test 5:
|   guest) # dd if=/dev/hwrng of=/dev/null
|   cancel dd process after 10 seconds
|   guest) # dd if=/dev/hwrng of=/dev/null &
|   hotunplug rng device from qemu monitor
|
| test 6:
|   use a fifo as rng backend, execute test 0 ~ 5 with no input of fifo

V5: reset cleanup_done flag, drop redundant init of reference count, use
    compiler barrier to prevent recording.
V4: update patch 4 to fix corrupt, decrease last reference for triggering
    the cleanup, fix unregister race pointed by Herbert
V3: initialize kref to 1
V2: added patch 2 to fix a deadlock, update current patch 3 to fix reference
    counting issue

Amos Kong (1):
  hw_random: move some code out mutex_lock for avoiding underlying
    deadlock

Rusty Russell (5):
  hw_random: place mutex around read functions and buffers.
  hw_random: use reference counts on each struct hwrng.
  hw_random: fix unregister race.
  hw_random: don't double-check old_rng.
  hw_random: don't init list element we're about to add to list.

 drivers/char/hw_random/core.c | 173 ++++++++++++++++++++++++++++++------------
 include/linux/hw_random.h     |   3 +
 2 files changed, 126 insertions(+), 50 deletions(-)

-- 
1.9.3