Re: [PATCH 3/3] migration/postcopy: replace have_listen_thread check with PostcopyState check

[Dr. David Alan Gilbert]

* Wei Yang (address@hidden) wrote:
> After previous cleanup, postcopy thread is running only when
> PostcopyState is LISTENNING or RUNNING. This means it is not necessary
> to spare a variable have_listen_thread to represent the state.
> 
> Replace the check on have_listen_thread with PostcopyState and remove
> the variable.
> 
> Signed-off-by: Wei Yang <address@hidden>
> ---
>  migration/migration.h | 1 -
>  migration/ram.c       | 2 +-
>  migration/ram.h       | 1 +
>  migration/savevm.c    | 4 +---
>  4 files changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/migration/migration.h b/migration/migration.h
> index 4f2fe193dc..a4d639663d 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -63,7 +63,6 @@ struct MigrationIncomingState {
>      /* Set this when we want the fault thread to quit */
>      bool           fault_thread_quit;
>  
> -    bool           have_listen_thread;
>      QemuThread     listen_thread;
>      QemuSemaphore  listen_thread_sem;
>  
> diff --git a/migration/ram.c b/migration/ram.c
> index 769d3f6454..dfc50d57d5 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -4188,7 +4188,7 @@ static bool postcopy_is_advised(void)
>      return ps >= POSTCOPY_INCOMING_ADVISE && ps < POSTCOPY_INCOMING_END;
>  }
>  
> -static bool postcopy_is_running(void)
> +bool postcopy_is_running(void)
>  {
>      PostcopyState ps = postcopy_state_get();
>      return ps >= POSTCOPY_INCOMING_LISTENING && ps < POSTCOPY_INCOMING_END;
> diff --git a/migration/ram.h b/migration/ram.h
> index bd0eee79b6..44fe4753ad 100644
> --- a/migration/ram.h
> +++ b/migration/ram.h
> @@ -59,6 +59,7 @@ int ram_postcopy_send_discard_bitmap(MigrationState *ms);
>  /* For incoming postcopy discard */
>  int ram_discard_range(const char *block_name, uint64_t start, size_t length);
>  int ram_postcopy_incoming_init(MigrationIncomingState *mis);
> +bool postcopy_is_running(void);
>  
>  void ram_handle_compressed(void *host, uint8_t ch, uint64_t size);
>  
> diff --git a/migration/savevm.c b/migration/savevm.c
> index dcad8897a3..2a0e0b94df 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1836,7 +1836,6 @@ static void *postcopy_ram_listen_thread(void *opaque)
>      qemu_loadvm_state_cleanup();
>  
>      rcu_unregister_thread();
> -    mis->have_listen_thread = false;
>      postcopy_state_set(POSTCOPY_INCOMING_END, NULL);

That now needs a big comment saying it must be the last thing in the
thread, because now it's got meaning that it's here.

>  
>      return NULL;
> @@ -1880,7 +1879,6 @@ static int 
> loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
>          return -1;
>      }
>  
> -    mis->have_listen_thread = true;
>      /* Start up the listening thread and wait for it to signal ready */
>      qemu_sem_init(&mis->listen_thread_sem, 0);
>      qemu_thread_create(&mis->listen_thread, "postcopy/listen",
> @@ -2518,7 +2516,7 @@ int qemu_loadvm_state(QEMUFile *f)
>  
>      trace_qemu_loadvm_state_post_main(ret);
>  
> -    if (mis->have_listen_thread) {
> +    if (postcopy_is_running()) {
>          /* Listen thread still going, can't clean up yet */
>          return ret;
>      }

Can you explain to me why this is afe in the case of a failure in
loadvm_postcopy_handle_listen between the start where it sets
the state to LISTENING, and the point where it currently sets
hasve_listen_thread ?  Wouldn't this cause qemu_loadvm_state
not to cleanup?

Dave

> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK