Re: [PATCH v2 1/1] multifd: Shut down the QIO channels to avoid blocking the send threads when they are terminated.

[Li Zhang <lizhang@suse.de>]

On 12/6/21 8:50 PM, Dr. David Alan Gilbert wrote:
> * Li Zhang (lizhang@suse.de) wrote:
>> Thanks for Daniel's review.
>>
>> Hi David and Juan,
>>
>> Any comments for this patch?
>>
> Yeh I think that's OK, so
>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>
> I'd have a slight preference for it being before the post I think.

Thanks.

>
> Dave
>
>> Thanks
>>
>> Li
>>
>> On 12/3/21 12:55 PM, Li Zhang wrote:
>>> When doing live migration with multifd channels 8, 16 or larger number,
>>> the guest hangs in the presence of the network errors such as missing TCP ACKs.
>>>
>>> At sender's side:
>>> The main thread is blocked on qemu_thread_join, migration_fd_cleanup
>>> is called because one thread fails on qio_channel_write_all when
>>> the network problem happens and other send threads are blocked on sendmsg.
>>> They could not be terminated. So the main thread is blocked on qemu_thread_join
>>> to wait for the threads terminated.
>>>
>>> (gdb) bt
>>> 0  0x00007f30c8dcffc0 in __pthread_clockjoin_ex () at /lib64/libpthread.so.0
>>> 1  0x000055cbb716084b in qemu_thread_join (thread=0x55cbb881f418) at ../util/qemu-thread-posix.c:627
>>> 2  0x000055cbb6b54e40 in multifd_save_cleanup () at ../migration/multifd.c:542
>>> 3  0x000055cbb6b4de06 in migrate_fd_cleanup (s=0x55cbb8024000) at ../migration/migration.c:1808
>>> 4  0x000055cbb6b4dfb4 in migrate_fd_cleanup_bh (opaque=0x55cbb8024000) at ../migration/migration.c:1850
>>> 5  0x000055cbb7173ac1 in aio_bh_call (bh=0x55cbb7eb98e0) at ../util/async.c:141
>>> 6  0x000055cbb7173bcb in aio_bh_poll (ctx=0x55cbb7ebba80) at ../util/async.c:169
>>> 7  0x000055cbb715ba4b in aio_dispatch (ctx=0x55cbb7ebba80) at ../util/aio-posix.c:381
>>> 8  0x000055cbb7173ffe in aio_ctx_dispatch (source=0x55cbb7ebba80, callback=0x0, user_data=0x0) at ../util/async.c:311
>>> 9  0x00007f30c9c8cdf4 in g_main_context_dispatch () at /usr/lib64/libglib-2.0.so.0
>>> 10 0x000055cbb71851a2 in glib_pollfds_poll () at ../util/main-loop.c:232
>>> 11 0x000055cbb718521c in os_host_main_loop_wait (timeout=42251070366) at ../util/main-loop.c:255
>>> 12 0x000055cbb7185321 in main_loop_wait (nonblocking=0) at ../util/main-loop.c:531
>>> 13 0x000055cbb6e6ba27 in qemu_main_loop () at ../softmmu/runstate.c:726
>>> 14 0x000055cbb6ad6fd7 in main (argc=68, argv=0x7ffc0c578888, envp=0x7ffc0c578ab0) at ../softmmu/main.c:50
>>>
>>> To make sure that the send threads could be terminated, IO channels should be
>>> shut down to avoid waiting IO.
>>>
>>> Signed-off-by: Li Zhang <lizhang@suse.de>
>>> ---
>>>    migration/multifd.c | 3 +++
>>>    1 file changed, 3 insertions(+)
>>>
>>> diff --git a/migration/multifd.c b/migration/multifd.c
>>> index 7c9deb1921..33f8287969 100644
>>> --- a/migration/multifd.c
>>> +++ b/migration/multifd.c
>>> @@ -523,6 +523,9 @@ static void multifd_send_terminate_threads(Error *err)
>>>            qemu_mutex_lock(&p->mutex);
>>>            p->quit = true;
>>>            qemu_sem_post(&p->sem);
>>> +        if (p->c) {
>>> +            qio_channel_shutdown(p->c, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
>>> +        }
>>>            qemu_mutex_unlock(&p->mutex);
>>>        }
>>>    }
>>