[PATCH] migration/tls: add error handling in multifd_tls_handshake_thread

[PATCH] migration/tls: add error handling in multifd_tls_handshake_thread

[Hao Wang]

If any error happens during multifd send thread creating (e.g. channel broke
because new domain is destroyed by the dst), multifd_tls_handshake_thread
may exit silently, leaving main migration thread hanging (ram_save_setup ->
multifd_send_sync_main -> qemu_sem_wait(&p->sem_sync)).
Fix that by adding error handling in multifd_tls_handshake_thread.

Signed-off-by: Hao Wang <wanghao232@huawei.com>
---
 migration/multifd.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index 45c690aa11..df29cdd26a 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -736,7 +736,16 @@ static void multifd_tls_outgoing_handshake(QIOTask *task,
     } else {
         trace_multifd_tls_outgoing_handshake_complete(ioc);
     }
-    multifd_channel_connect(p, ioc, err);
+
+    if (multifd_channel_connect(p, ioc, err)) {
+        /*
+         * Error happen, mark multifd_send_thread status as 'quit' although it
+         * is not created, and then tell who pay attention to me.
+         */
+        p->quit = true;
+        qemu_sem_post(&multifd_send_state->channels_ready);
+        qemu_sem_post(&p->sem_sync);
+    }
 }
 
 static void *multifd_tls_handshake_thread(void *opaque)
-- 
2.23.0

Re: [PATCH] migration/tls: add error handling in multifd_tls_handshake_thread

[Daniel P. Berrangé]

On Tue, Feb 09, 2021 at 03:52:51PM +0800, Hao Wang wrote:
> If any error happens during multifd send thread creating (e.g. channel broke
> because new domain is destroyed by the dst), multifd_tls_handshake_thread
> may exit silently, leaving main migration thread hanging (ram_save_setup ->
> multifd_send_sync_main -> qemu_sem_wait(&p->sem_sync)).
> Fix that by adding error handling in multifd_tls_handshake_thread.
> 
> Signed-off-by: Hao Wang <wanghao232@huawei.com>
> ---
>  migration/multifd.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 45c690aa11..df29cdd26a 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -736,7 +736,16 @@ static void multifd_tls_outgoing_handshake(QIOTask *task,
>      } else {
>          trace_multifd_tls_outgoing_handshake_complete(ioc);
>      }
> -    multifd_channel_connect(p, ioc, err);
> +
> +    if (multifd_channel_connect(p, ioc, err)) {

Urgh, this method is rather confusing usng "true" to indicate failure.
In include/qapi/error.h we document

  • bool-valued functions return true on success / false on failure,

Admittedly this problem is pre-existing before this patch, but I
would none the less like to see a patch that fixes thse inverted
semantics first, and then this as a subsequent patch on top.

> +        /*
> +         * Error happen, mark multifd_send_thread status as 'quit' although it
> +         * is not created, and then tell who pay attention to me.
> +         */
> +        p->quit = true;
> +        qemu_sem_post(&multifd_send_state->channels_ready);
> +        qemu_sem_post(&p->sem_sync);
> +    }
>  }
>  
>  static void *multifd_tls_handshake_thread(void *opaque)

Regards,
Daniel
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