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[Qemu-devel] [PATCH 2/2] cpus: be more paranoid in avoiding deadlocks
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 2/2] cpus: be more paranoid in avoiding deadlocks |
Date: |
Fri, 27 Feb 2015 20:05:51 +0100 |
For good measure, ensure that the following sequence:
thread 1 calls qemu_mutex_lock_iothread
thread 2 calls qemu_mutex_lock_iothread
VCPU thread are created
VCPU thread enters execution loop
results in the VCPU threads letting the other two threads run
and obeying iothread_requesting_mutex even if the VCPUs are
not halted. To do this, check iothread_requesting_mutex
before execution starts.
I could not reproduce this problem; it was only found by
inspection.
Signed-off-by: Paolo Bonzini <address@hidden>
---
cpus.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/cpus.c b/cpus.c
index 83c078e..0fac143 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1025,6 +1025,9 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
}
}
+ /* process any pending work */
+ exit_request = 1;
+
while (1) {
tcg_exec_all();
@@ -1115,10 +1118,11 @@ bool qemu_in_vcpu_thread(void)
void qemu_mutex_lock_iothread(void)
{
+ atomic_inc(&iothread_requesting_mutex);
if (!tcg_enabled() || !first_cpu) {
qemu_mutex_lock(&qemu_global_mutex);
+ atomic_dec(&iothread_requesting_mutex);
} else {
- atomic_inc(&iothread_requesting_mutex);
if (qemu_mutex_trylock(&qemu_global_mutex)) {
qemu_cpu_kick_thread(first_cpu);
qemu_mutex_lock(&qemu_global_mutex);
--
2.3.0