Re: [PATCH 2/2] migration: Fix return-path thread exit

["Cédric Le Goater" <clg@redhat.com>]

On 2/2/24 15:42, Fabiano Rosas wrote:
> Cédric Le Goater <clg@redhat.com> writes:
> 
>> In case of error, close_return_path_on_source() can perform a shutdown
>> to exit the return-path thread.  However, in migrate_fd_cleanup(),
>> 'to_dst_file' is closed before calling close_return_path_on_source()
>> and the shutdown fails, leaving the source and destination waiting for
>> an event to occur.
> 
> At close_return_path_on_source, qemu_file_shutdown() and checking
> ms->to_dst_file are done under the qemu_file_lock, so how could
> migrate_fd_cleanup() have cleared the pointer but the ms->to_dst_file
> check have passed?

This is not a locking issue, it's much simpler. migrate_fd_cleanup()
clears the ms->to_dst_file pointer and closes the QEMUFile and then
calls close_return_path_on_source() which then tries to use resources
which are not available anymore.

Thanks,

C.




> 
>>
>> Close the file after calling close_return_path_on_source() so that the
>> shutdown succeeds and the return-path thread exits.
>>
>> Signed-off-by: Cédric Le Goater <clg@redhat.com>
>> ---
>>   migration/migration.c | 12 +++++-------
>>   1 file changed, 5 insertions(+), 7 deletions(-)
>>
>> diff --git a/migration/migration.c b/migration/migration.c
>> index 2c3362235c7651c11d581f3c3639571f1f9636ef..1e0b6acaedc272e8ce26ad40be2c42177f5fd14e 100644
>> --- a/migration/migration.c
>> +++ b/migration/migration.c
>> @@ -1314,6 +1314,7 @@ void migrate_set_state(int *state, int old_state, int new_state)
>>   static void migrate_fd_cleanup(MigrationState *s)
>>   {
>>       int file_error = 0;
>> +    QEMUFile *tmp = NULL;
>>   
>>       g_free(s->hostname);
>>       s->hostname = NULL;
>> @@ -1323,8 +1324,6 @@ static void migrate_fd_cleanup(MigrationState *s)
>>       qemu_savevm_state_cleanup();
>>   
>>       if (s->to_dst_file) {
>> -        QEMUFile *tmp;
>> -
>>           trace_migrate_fd_cleanup();
>>           bql_unlock();
>>           if (s->migration_thread_running) {
>> @@ -1344,15 +1343,14 @@ static void migrate_fd_cleanup(MigrationState *s)
>>            * critical section won't block for long.
>>            */
>>           migration_ioc_unregister_yank_from_file(tmp);
>> -        qemu_fclose(tmp);
>>       }
>>   
>> -    /*
>> -     * We already cleaned up to_dst_file, so errors from the return
>> -     * path might be due to that, ignore them.
>> -     */
>>       close_return_path_on_source(s, file_error);
>>   
>> +    if (tmp) {
>> +        qemu_fclose(tmp);
>> +    }
>> +
>>       assert(!migration_is_active(s));
>>   
>>       if (s->state == MIGRATION_STATUS_CANCELLING) {
>