The drain_rcu_call() function can be blocked as long as an RCU reader
stays in a read-side critical section. This is typically what happens
when a TCG vCPU is executing a busy loop. It can deadlock the QEMU
monitor as reported inhttps://gitlab.com/qemu-project/qemu/-/issues/650 .
This can be avoided by allowing drain_rcu_call() to enforce an RCU grace
period. Since each reader might need to do specific actions to end a
read-side critical section, do it with notifiers.
Prepare ground for this by adding a notifier list to the RCU reader
struct and use it in wait_for_readers() if drain_rcu_call() is in
progress. An API is added for readers to register their notifiers.
This is largely based on a draft from Paolo Bonzini.
Suggested-by: Paolo Bonzini<pbonzini@redhat.com>
Signed-off-by: Greg Kurz<groug@kaod.org>
---
include/qemu/rcu.h | 15 +++++++++++++++
util/rcu.c | 19 +++++++++++++++++++
2 files changed, 34 insertions(+)