Patchwork [v3,1/4] migration: notify migration state before starting thread

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Submitter Stefan Hajnoczi
Date July 29, 2013, 1:01 p.m.
Message ID <1375102920-18817-2-git-send-email-stefanha@redhat.com>
Download mbox | patch
Permalink /patch/262756/
State New
Headers show

Comments

Stefan Hajnoczi - July 29, 2013, 1:01 p.m.
The migration thread runs outside the QEMU global mutex when possible.
Therefore we must notify migration state change *before* starting the
migration thread.

This allows registered listeners to act before live migration iterations
begin.  Therefore they can get into a state that allows for live
migration.  When the migration thread starts everything will be ready.

Without this patch there is a race condition during migration setup,
depending on whether the migration thread has already transitioned from
SETUP to ACTIVE state.

Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 migration.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Patch

diff --git a/migration.c b/migration.c
index e12e784..a5ed26b 100644
--- a/migration.c
+++ b/migration.c
@@ -658,7 +658,9 @@  void migrate_fd_connect(MigrationState *s)
     qemu_file_set_rate_limit(s->file,
                              s->bandwidth_limit / XFER_LIMIT_RATIO);
 
+    /* Notify before starting migration thread */
+    notifier_list_notify(&migration_state_notifiers, s);
+
     qemu_thread_create(&s->thread, migration_thread, s,
                        QEMU_THREAD_JOINABLE);
-    notifier_list_notify(&migration_state_notifiers, s);
 }