Re: [Qemu-devel] [PATCH 14/16] cpus-common: Introduce async_safe_run_on_cpu()

[Alex Bennée]

Paolo Bonzini <address@hidden> writes:

> Signed-off-by: Paolo Bonzini <address@hidden>

Reviewed-by: Alex Bennée <address@hidden>

> ---
>  cpus-common.c     | 33 +++++++++++++++++++++++++++++++--
>  include/qom/cpu.h | 14 ++++++++++++++
>  2 files changed, 45 insertions(+), 2 deletions(-)
>
> diff --git a/cpus-common.c b/cpus-common.c
> index 429652c..38b1d55 100644
> --- a/cpus-common.c
> +++ b/cpus-common.c
> @@ -18,6 +18,7 @@
>   */
>
>  #include "qemu/osdep.h"
> +#include "qemu/main-loop.h"
>  #include "exec/cpu-common.h"
>  #include "qom/cpu.h"
>  #include "sysemu/cpus.h"
> @@ -106,7 +107,7 @@ struct qemu_work_item {
>      struct qemu_work_item *next;
>      run_on_cpu_func func;
>      void *data;
> -    bool free, done;
> +    bool free, exclusive, done;
>  };
>
>  static void queue_work_on_cpu(CPUState *cpu, struct qemu_work_item *wi)
> @@ -139,6 +140,7 @@ void do_run_on_cpu(CPUState *cpu, run_on_cpu_func func, 
> void *data,
>      wi.data = data;
>      wi.done = false;
>      wi.free = false;
> +    wi.exclusive = false;
>
>      queue_work_on_cpu(cpu, &wi);
>      while (!atomic_mb_read(&wi.done)) {
> @@ -229,6 +231,19 @@ void cpu_exec_end(CPUState *cpu)
>      qemu_mutex_unlock(&qemu_cpu_list_lock);
>  }
>
> +void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data)
> +{
> +    struct qemu_work_item *wi;
> +
> +    wi = g_malloc0(sizeof(struct qemu_work_item));
> +    wi->func = func;
> +    wi->data = data;
> +    wi->free = true;
> +    wi->exclusive = true;
> +
> +    queue_work_on_cpu(cpu, wi);
> +}
> +
>  void process_queued_cpu_work(CPUState *cpu)
>  {
>      struct qemu_work_item *wi;
> @@ -245,7 +260,21 @@ void process_queued_cpu_work(CPUState *cpu)
>              cpu->queued_work_last = NULL;
>          }
>          qemu_mutex_unlock(&cpu->work_mutex);
> -        wi->func(cpu, wi->data);
> +        if (wi->exclusive) {
> +            /* Running work items outside the BQL avoids the following 
> deadlock:
> +             * 1) start_exclusive() is called with the BQL taken while 
> another
> +             * CPU is running; 2) cpu_exec in the other CPU tries to takes 
> the
> +             * BQL, so it goes to sleep; start_exclusive() is sleeping too, 
> so
> +             * neither CPU can proceed.
> +             */
> +            qemu_mutex_unlock_iothread();
> +            start_exclusive();
> +            wi->func(cpu, wi->data);
> +            end_exclusive();
> +            qemu_mutex_lock_iothread();
> +        } else {
> +            wi->func(cpu, wi->data);
> +        }
>          qemu_mutex_lock(&cpu->work_mutex);
>          if (wi->free) {
>              g_free(wi);
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 934c07a..4092dd9 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -656,6 +656,20 @@ void run_on_cpu(CPUState *cpu, run_on_cpu_func func, 
> void *data);
>  void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data);
>
>  /**
> + * async_safe_run_on_cpu:
> + * @cpu: The vCPU to run on.
> + * @func: The function to be executed.
> + * @data: Data to pass to the function.
> + *
> + * Schedules the function @func for execution on the vCPU @cpu 
> asynchronously,
> + * while all other vCPUs are sleeping.
> + *
> + * Unlike run_on_cpu and async_run_on_cpu, the function is run outside the
> + * BQL.
> + */
> +void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data);
> +
> +/**
>   * qemu_get_cpu:
>   * @index: The address@hidden value of the CPU to obtain.
>   *


--
Alex Bennée