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[PATCH 2/5] migration: Shutdown src in await_return_path_close_on_source

From: Peter Xu
Subject: [PATCH 2/5] migration: Shutdown src in await_return_path_close_on_source()
Date: Tue, 20 Jul 2021 21:21:31 -0400

We have a logic in await_return_path_close_on_source() that we will explicitly
shutdown the socket when migration encounters errors.  However it could be racy
because from_dst_file could have been reset right after checking it but before
passing it to qemu_file_shutdown() by the rp_thread.

Fix it by shutdown() on the src file instead.  Since they must be a pair of
qemu files, shutdown on either of them will work the same.

Since at it, drop the check for from_dst_file directly, which makes the
behavior even more predictable.

Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
 migration/migration.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 21b94f75a3..4f48cde796 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2882,12 +2882,15 @@ static int 
await_return_path_close_on_source(MigrationState *ms)
      * rp_thread will exit, however if there's an error we need to cause
      * it to exit.
-    if (qemu_file_get_error(ms->to_dst_file) && ms->rp_state.from_dst_file) {
+    if (qemu_file_get_error(ms->to_dst_file)) {
          * shutdown(2), if we have it, will cause it to unblock if it's stuck
-         * waiting for the destination.
+         * waiting for the destination.  We do shutdown on to_dst_file should
+         * also shutdown the from_dst_file as they're in a pair. We explicilty
+         * don't operate on from_dst_file because it's potentially racy
+         * (rp_thread could have reset it in parallel).
-        qemu_file_shutdown(ms->rp_state.from_dst_file);
+        qemu_file_shutdown(ms->to_dst_file);

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