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cpus: run work items for all vCPUs if single-threaded

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This avoids the following I/O thread deadlock:

1) the I/O thread calls run_on_cpu for CPU 3 from a timer.  single_tcg_halt_cond
is signaled

2) CPU 1 is running and exits.  It finds no work item and enters CPU 2

3) because the I/O thread is stuck in run_on_cpu, the round-robin kick
timer never triggers, and CPU 3 never runs the work item

4) run_on_cpu never completes

Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2018-11-14 12:36:57 +01:00
parent d98f26073b
commit a8efa60633
1 changed files with 8 additions and 4 deletions
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10
cpus.c
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@ -1220,16 +1220,20 @@ static void qemu_wait_io_event_common(CPUState *cpu)
process_queued_cpu_work(cpu); process_queued_cpu_work(cpu);
} }
static void qemu_tcg_rr_wait_io_event(CPUState *cpu) static void qemu_tcg_rr_wait_io_event(void)
{ {
CPUState *cpu;
while (all_cpu_threads_idle()) { while (all_cpu_threads_idle()) {
stop_tcg_kick_timer(); stop_tcg_kick_timer();
qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex); qemu_cond_wait(first_cpu->halt_cond, &qemu_global_mutex);
} }
start_tcg_kick_timer(); start_tcg_kick_timer();
CPU_FOREACH(cpu) {
qemu_wait_io_event_common(cpu); qemu_wait_io_event_common(cpu);
}
} }
static void qemu_wait_io_event(CPUState *cpu) static void qemu_wait_io_event(CPUState *cpu)
@ -1562,7 +1566,7 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg)
qemu_notify_event(); qemu_notify_event();
} }
qemu_tcg_rr_wait_io_event(cpu ? cpu : first_cpu); qemu_tcg_rr_wait_io_event();
deal_with_unplugged_cpus(); deal_with_unplugged_cpus();
} }