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

[Dr. David Alan Gilbert]

* Wei Yang (address@hidden) wrote:
> On Tue, Oct 08, 2019 at 08:15:51PM +0100, Dr. David Alan Gilbert wrote:
> >* 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?
> >
> 
> 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!

Dave

> >Dave
> >
> >> -- 
> >> 2.17.1
> >> 
> >--
> >Dr. David Alan Gilbert / address@hidden / Manchester, UK
> 
> -- 
> Wei Yang
> Help you, Help me
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK