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[82.29.237.198]) by smtp.gmail.com with ESMTPSA id j1sm118340wms.7.2021.07.12.10.44.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jul 2021 10:44:44 -0700 (PDT) Date: Mon, 12 Jul 2021 18:44:42 +0100 From: "Dr. David Alan Gilbert" To: Peter Xu Subject: Re: [PATCH 1/3] migration: Release return path early for paused postcopy Message-ID: References: <20210708190653.252961-1-peterx@redhat.com> <20210708190653.252961-2-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210708190653.252961-2-peterx@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Lukas Straub , Juan Quintela , Li Xiaohui , qemu-devel@nongnu.org, Li Xiaohui , Leonardo Bras Soares Passos Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Xu (peterx@redhat.com) wrote: > 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 Reviewed-by: Dr. David Alan Gilbert (and I can cleanup the email address problem) > --- > migration/migration.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/migration/migration.c b/migration/migration.c > index 5ff7ba9d5c..8786104c9a 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; > } > -- > 2.31.1 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK