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

[Wei Yang <richardw.yang@linux.intel.com>]

On Wed, Oct 09, 2019 at 11:17:16AM +0100, Dr. David Alan Gilbert wrote:
>* Wei Yang (richardw.yang@linux.intel.com) wrote:
>> On Tue, Oct 08, 2019 at 08:15:51PM +0100, Dr. David Alan Gilbert wrote:
>> >* Wei Yang (richardw.yang@linux.intel.com) 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 <richardw.yang@linux.intel.com>
>> >> ---
>> >>  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?
>> >
>> 
>> I have to say you are right.  listen_thread may not started when PostcopyState
>> is already set to LISTENING.
>> 
>> The ugly fix may be set PostcopyState back to original one. Not sure whether
>> you would like this. 
>
>I think the 'have_listen_thread' might be the simplest solution though;
>it's very simple!
>

Yep, you are right.

>Dave
>
>> >Dave
>> >
>> >> -- 
>> >> 2.17.1
>> >> 
>> >--
>> >Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>> 
>> -- 
>> Wei Yang
>> Help you, Help me
>--
>Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

-- 
Wei Yang
Help you, Help me