Unmapping a blob changes the memory map, which is protected with RCU.
RCU is designed to minimize the read-side overhead at the cost of
reclamation delay. While this design usually makes sense, it is
problematic when unmapping a blob because the operation blocks all
virtio-gpu commands and causes perceivable disruption.

Minimize such the disruption with force_rcu(), which minimizes the
reclamation delay at the cost of a read-side overhead.

Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
---
Changes in v2:
- Stopped overloading the call_rcu1() and force_rcu() notifications onto
  one event. This fixes a deadlock after try_dequeue() caused by
  incorrect masking of call_rcu1() notifications, and eliminates
  spurious force quiescent states caused by being confused with a
  call_rcu1() notification.
  Tested-by: from the previous version was not collected because this
  changes the logic significantly.
- Merged the rcu_call_count and forced variables into one to avoid
  the race between them that used to require a loop to resolve.
- Aligned the type of the duration variable in qemu_futex_timedwait()
  for Windows.
- Fixed timespec of qemu_futex_timedwait() for 32-bit Linux.
- Link to v1: https://lore.kernel.org/qemu-devel/20251029-force_rcu-v1-0-bf860a6277a6@rsg.ci.i.u-tokyo.ac.jp

---
Akihiko Odaki (6):
      timer: Rename init_clocks() to qemu_clock_init()
      futex: Add qemu_futex_timedwait()
      qemu-thread: Add qemu_event_timedwait()
      rcu: Use call_rcu() in synchronize_rcu()
      rcu: Wake the RCU thread when draining
      virtio-gpu: Force RCU when unmapping blob

 include/qemu/futex.h              | 34 ++++++++++++--
 include/qemu/rcu.h                |  1 +
 include/qemu/thread-posix.h       | 11 +++++
 include/qemu/thread.h             |  8 +++-
 include/qemu/timer.h              |  4 +-
 hw/display/virtio-gpu-virgl.c     |  1 +
 tests/unit/test-aio-multithread.c |  2 +-
 util/event.c                      | 28 +++++++++--
 util/main-loop.c                  |  2 +-
 util/qemu-thread-posix.c          | 11 +----
 util/qemu-timer.c                 |  7 +--
 util/rcu.c                        | 98 ++++++++++++++++++++++-----------------
 12 files changed, 137 insertions(+), 70 deletions(-)
---
base-commit: 466e779e05b5087bffe39ecc51ec97fdf9121e8b
change-id: 20251027-force_rcu-616c743373f7

Best regards,
--  
Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>