From 2e3e3da3c2ad559d1255a9a3bf3df0782c2cf231 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Thu, 8 Jul 2021 15:06:51 -0400 Subject: [PATCH] migration: Release return path early for paused postcopy When postcopy pause triggered, we rely on the migration thread to cleanup the to_dst_file handle, and the return path thread to cleanup the from_dst_file handle (which is stored in the local variable "rp"). Within the process, from_dst_file cleanup (qemu_fclose) is postponed until it's setup again due to a postcopy recovery. It used to work before yank was born; after yank is introduced we rely on the refcount of IOC to correctly unregister yank function in channel_close(). If without the early and on-time release of from_dst_file handle the yank function will be leftover during paused postcopy. Without this patch, below steps (quoted from Xiaohui) could trigger qemu src crash: 1.Boot vm on src host 2.Boot vm on dst host 3.Enable postcopy on src&dst host 4.Load stressapptest in vm and set postcopy speed to 50M 5.Start migration from src to dst host, change into postcopy mode when migration is active. 6.When postcopy is active, down the network card(do migration via this network) on dst host. 7.Wait untill postcopy is paused on src&dst host. 8.Before up network card, recover migration on dst host, will get error like following. 9.Ignore the error of step 8, go on recovering migration on src host: After step 9, qemu on src host will core dump after some seconds: qemu-kvm: ../util/yank.c:107: yank_unregister_instance: Assertion `QLIST_EMPTY(&entry->yankfns)' failed. 1.sh: line 38: 44662 Aborted (core dumped) Reported-by: Li Xiaohui Signed-off-by: Peter Xu Message-Id: <20210708190653.252961-2-peterx@redhat.com> Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Dr. David Alan Gilbert --- migration/migration.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/migration/migration.c b/migration/migration.c index d717cd089a..38ebc6c1ab 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -2818,12 +2818,12 @@ out: * Maybe there is something we can do: it looks like a * network down issue, and we pause for a recovery. */ + qemu_fclose(rp); + ms->rp_state.from_dst_file = NULL; + rp = NULL; if (postcopy_pause_return_path_thread(ms)) { /* Reload rp, reset the rest */ - if (rp != ms->rp_state.from_dst_file) { - qemu_fclose(rp); - rp = ms->rp_state.from_dst_file; - } + rp = ms->rp_state.from_dst_file; ms->rp_state.error = false; goto retry; }