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cpus: be more paranoid in avoiding deadlocks

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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.

Tested-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-02-27 20:01:03 +01:00
parent 6b49809c59
commit 21618b3e55
1 changed files with 5 additions and 1 deletions
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6
cpus.c
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@ -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);