Commit 7bed89958bfb ("device_core: use drain_call_rcu in in qmp_device_add")
introduced a regression in QEMU 6.0 : passing device_add without argument
hangs the monitor. This was reported against qemu-system-mips64 with TGC,
but I could consistently reproduce it with other targets (x86 and ppc64).See https://gitlab.com/qemu-project/qemu/-/issues/650 for details. The problem is that an emulated busy-looping vCPU can stay forever in its RCU read-side critical section and prevent drain_call_rcu() to return. This series fixes the issue by letting RCU kick vCPUs out of the read-side critical section when drain_call_rcu() is in progress. This is achieved through notifiers, as suggested by Paolo Bonzini. v2: - moved notifier list to RCU reader data - separate API for notifier registration - CPUState passed as an opaque pointer Greg Kurz (2): rcu: Introduce force_rcu notifier accel/tcg: Register a force_rcu notifier accel/tcg/tcg-accel-ops-mttcg.c | 3 +++ accel/tcg/tcg-accel-ops-rr.c | 3 +++ accel/tcg/tcg-accel-ops.c | 15 +++++++++++++++ accel/tcg/tcg-accel-ops.h | 2 ++ include/qemu/rcu.h | 16 ++++++++++++++++ util/rcu.c | 22 +++++++++++++++++++++- 6 files changed, 60 insertions(+), 1 deletion(-) -- 2.31.1
