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.

v3->v4: fix upgrade and add a test for that, too

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 (2):
  coroutine-lock: reimplement CoRwLock to fix downgrade bug
  test-coroutine: add rwlock upgrade test

 block/vdi.c                 |  11 ++-
 include/qemu/coroutine.h    |  17 ++--
 tests/unit/test-coroutine.c | 161 ++++++++++++++++++++++++++++++++++++
 util/qemu-coroutine-lock.c  | 149 +++++++++++++++++++++------------
 4 files changed, 274 insertions(+), 64 deletions(-)

-- 
2.29.2