[PULL 21/42] migration/multifd: Make multifd_send() thread safe

["Cédric Le Goater" <clg@redhat.com>]

From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>

multifd_send() function is currently not thread safe, make it thread safe
by holding a lock during its execution.

This way it will be possible to safely call it concurrently from multiple
threads.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Link: https://lore.kernel.org/qemu-devel/dd0f3bcc02ca96a7d523ca58ea69e495a33b453b.1741124640.git.maciej.szmigiero@oracle.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 migration/multifd.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/migration/multifd.c b/migration/multifd.c
index 01f427d8ed036417559a0573d369172f72b508e1..add6f86175c25c0f7925a919c267240826fab54c 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -50,6 +50,10 @@ typedef struct {
 
 struct {
     MultiFDSendParams *params;
+
+    /* multifd_send() body is not thread safe, needs serialization */
+    QemuMutex multifd_send_mutex;
+
     /*
      * Global number of generated multifd packets.
      *
@@ -339,6 +343,8 @@ bool multifd_send(MultiFDSendData **send_data)
         return false;
     }
 
+    QEMU_LOCK_GUARD(&multifd_send_state->multifd_send_mutex);
+
     /* We wait here, until at least one channel is ready */
     qemu_sem_wait(&multifd_send_state->channels_ready);
 
@@ -507,6 +513,7 @@ static void multifd_send_cleanup_state(void)
     socket_cleanup_outgoing_migration();
     qemu_sem_destroy(&multifd_send_state->channels_created);
     qemu_sem_destroy(&multifd_send_state->channels_ready);
+    qemu_mutex_destroy(&multifd_send_state->multifd_send_mutex);
     g_free(multifd_send_state->params);
     multifd_send_state->params = NULL;
     g_free(multifd_send_state);
@@ -887,6 +894,7 @@ bool multifd_send_setup(void)
     thread_count = migrate_multifd_channels();
     multifd_send_state = g_malloc0(sizeof(*multifd_send_state));
     multifd_send_state->params = g_new0(MultiFDSendParams, thread_count);
+    qemu_mutex_init(&multifd_send_state->multifd_send_mutex);
     qemu_sem_init(&multifd_send_state->channels_created, 0);
     qemu_sem_init(&multifd_send_state->channels_ready, 0);
     qatomic_set(&multifd_send_state->exiting, 0);
-- 
2.48.1