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[PATCH v2 0/2] accel/tcg: Fix monitor deadlock
From: |
Greg Kurz |
Subject: |
[PATCH v2 0/2] accel/tcg: Fix monitor deadlock |
Date: |
Tue, 19 Oct 2021 07:56:30 +0200 |
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
- [PATCH v2 0/2] accel/tcg: Fix monitor deadlock,
Greg Kurz <=