This is a resubmit of David Edmondson's series at
https://patchew.org/QEMU/20210309144015.557477-1-david.edmondson@oracle.com/.
After closer analysis on IRC, the CoRwLock's attempt to ensure
fairness turned out to be flawed.  Therefore, this series
reimplements CoRwLock without using a CoQueue.  Tracking whether
each queued coroutine is a reader/writer makes it possible to
never wake a writer when only readers should be allowed and
vice versa.

David Edmondson (4):
  block/vdi: When writing new bmap entry fails, don't leak the buffer
  block/vdi: Don't assume that blocks are larger than VdiHeader
  coroutine/mutex: Store the coroutine in the CoWaitRecord only once
  test-coroutine: Add rwlock downgrade test

Paolo Bonzini (1):
  coroutine-lock: reimplement CoRwLock to fix downgrade bug

 block/vdi.c                 |  11 ++-
 include/qemu/coroutine.h    |  10 ++-
 tests/unit/test-coroutine.c | 112 ++++++++++++++++++++++++++
 util/qemu-coroutine-lock.c  | 151 +++++++++++++++++++++++-------------
 4 files changed, 225 insertions(+), 59 deletions(-)

-- 
2.29.2