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

[Wei Yang]

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. 

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

-- 
Wei Yang
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