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Tue, 19 May 2020 10:24:24 +0000 (UTC) Date: Tue, 19 May 2020 11:24:22 +0100 From: "Dr. David Alan Gilbert" To: Dima Stepanov Subject: Re: [PATCH v2 5/5] vhost: add device started check in migration set log Message-ID: <20200519102422.GC2798@work-vm> References: <20200512093521.GA5363@dimastep-nix> <20200512235934-mutt-send-email-mst@kernel.org> <20200513094703.GA15906@dimastep-nix> <722839b2-9412-b768-3ce6-d1b697d6d5dd@redhat.com> <20200515165449.GA1627@dimastep-nix> <553370a5-926b-d9c4-a8ec-8bdc07c94e6e@redhat.com> <20200518094053.GA6552@dimastep-nix> <20200518095359.GB2786@work-vm> <20200519090735.GA17826@dimastep-nix> MIME-Version: 1.0 In-Reply-To: <20200519090735.GA17826@dimastep-nix> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/19 00:34:39 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, T_HK_NAME_DR=0.01, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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: fam@euphon.net, kwolf@redhat.com, yc-core@yandex-team.ru, qemu-block@nongnu.org, "Michael S. Tsirkin" , Jason Wang , qemu-devel@nongnu.org, raphael.norwitz@nutanix.com, arei.gonglei@huawei.com, fengli@smartx.com, stefanha@redhat.com, marcandre.lureau@redhat.com, pbonzini@redhat.com, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Dima Stepanov (dimastep@yandex-team.ru) wrote: > On Mon, May 18, 2020 at 10:53:59AM +0100, Dr. David Alan Gilbert wrote: > > * Dima Stepanov (dimastep@yandex-team.ru) wrote: > > > On Mon, May 18, 2020 at 10:50:39AM +0800, Jason Wang wrote: > > > > > > > > On 2020/5/16 上午12:54, Dima Stepanov wrote: > > > > >On Thu, May 14, 2020 at 03:34:24PM +0800, Jason Wang wrote: > > > > >>On 2020/5/13 下午5:47, Dima Stepanov wrote: > > > > >>>>> case CHR_EVENT_CLOSED: > > > > >>>>> /* a close event may happen during a read/write, but vhost > > > > >>>>> * code assumes the vhost_dev remains setup, so delay the > > > > >>>>> * stop & clear to idle. > > > > >>>>> * FIXME: better handle failure in vhost code, remove bh > > > > >>>>> */ > > > > >>>>> if (s->watch) { > > > > >>>>> AioContext *ctx = qemu_get_current_aio_context(); > > > > >>>>> > > > > >>>>> g_source_remove(s->watch); > > > > >>>>> s->watch = 0; > > > > >>>>> qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, NULL, NULL, > > > > >>>>> NULL, NULL, false); > > > > >>>>> > > > > >>>>> aio_bh_schedule_oneshot(ctx, chr_closed_bh, opaque); > > > > >>>>> } > > > > >>>>> break; > > > > >>>>> > > > > >>>>>I think it's time we dropped the FIXME and moved the handling to common > > > > >>>>>code. Jason? Marc-André? > > > > >>>>I agree. Just to confirm, do you prefer bh or doing changes like what is > > > > >>>>done in this series? It looks to me bh can have more easier codes. > > > > >>>Could it be a good idea just to make disconnect in the char device but > > > > >>>postphone clean up in the vhost-user-blk (or any other vhost-user > > > > >>>device) itself? So we are moving the postphone logic and decision from > > > > >>>the char device to vhost-user device. One of the idea i have is as > > > > >>>follows: > > > > >>> - Put ourself in the INITIALIZATION state > > > > >>> - Start these vhost-user "handshake" commands > > > > >>> - If we got a disconnect error, perform disconnect, but don't clean up > > > > >>> device (it will be clean up on the roll back). I can be done by > > > > >>> checking the state in vhost_user_..._disconnect routine or smth like it > > > > >> > > > > >>Any issue you saw just using the aio bh as Michael posted above. > > > > >> > > > > >>Then we don't need to deal with the silent vhost_dev_stop() and we will have > > > > >>codes that is much more easier to understand. > > > > >I've implemented this solution inside > > > > >hw/block/vhost-user-blk.c:vhost_user_blk_event() in the similar way by > > > > >using the s->connected field. Looks good and more correct fix ). I have > > > > >two questions here before i'll rework the fixes: > > > > >1. Is it okay to make the similar fix inside vhost_user_blk_event() or > > > > >we are looking for more generic vhost-user solution? What do you think? > > > > > > > > > > > > I think I agree with Michael, it's better to have a generic vhost-user > > > > solution. But if it turns out to be not easy, we can start from fixing > > > > vhost-user-blk. > > > I also agree, but as i see it right now the connect/disconnect events > > > are handled inside each vhost-user device implementation file. So it will > > > need some global refactoring. So i suggest having this fix first and > > > after it refactoring the code: > > > - more devices will be involved > > > - i see there is some difference in device handling > > > > I'm following bits of this discussion, some thoughts; > > if your device doesn't support reconnect, then if, at the start of > > migration you find that you can't start the log what is the correct > > behaviour? > I'm not sure here, but it looks like that in this case the device state > will be: > disconnect -> stopped (will not be changed during migration, because > reconnect isn't supported) > And because of it the device state will not be changed during migration, > so there is no need for log and migration could be completed > successfully. > So as i see it (i could be wrong here) that: > - it is okay: if device is not started and we will not change this > state during migration + log start is failed > - it is not okay: if device is started + log start is failed (because > we can't handle the dirty pages and so on during migration) Yes, that does make sense to me. > > You can't carry on with the migration because you'd have an > > inconsistent migration state; so I guess that's why the abort() is there > > - but I think I'd generally prefer to fail the migration and hope the > > vhsot device is still working for anything other than the log. > > > > You're going to have to be pretty careful with the ordering of reconect > > - reconnecting on the source during a migration sounds pretty hairy, but > > a migration can take many minutes, so if you really want to survive this > > I guess you have to. > Maybe if we get a disconnect during migration then we could postphone or > just don't make reconnect at all till the end of migration on the source > side. This will make a device left in the stopped state. Yes, that's the easiest way, but you may find people object to it being out for that long. Dave > Thanks, Dima. > > > > > Dave > > > > > > > > > > > > > > > > >2. For migration we require an additional information that for the > > > > >vhost-user device it isn't an error, because i'm trigerring the > > > > >following assert error: > > > > > Core was generated by `x86_64-softmmu/qemu-system-x86_64 -nodefaults -no-user-config -M q35,sata=false'. > > > > > Program terminated with signal SIGABRT, Aborted. > > > > > #0 0x00007fb56e729428 in raise () from /lib/x86_64-linux-gnu/libc.so.6 > > > > > [Current thread is 1 (Thread 0x7fb486ef5700 (LWP 527734))] > > > > > > > > > > (gdb) bt > > > > > #0 0x00007fb56e729428 in raise () from /lib/x86_64-linux-gnu/libc.so.6 > > > > > #1 0x00007fb56e72b02a in abort () from /lib/x86_64-linux-gnu/libc.so.6 > > > > > #2 0x00005648ea376ee6 in vhost_log_global_start > > > > > (listener=0x5648ece4eb08) at ./hw/virtio/vhost.c:857 > > > > > #3 0x00005648ea2dde7e in memory_global_dirty_log_start () > > > > > at ./memory.c:2611 > > > > > #4 0x00005648ea2e68e7 in ram_init_bitmaps (rs=0x7fb4740008c0) > > > > > at ./migration/ram.c:2305 > > > > > #5 0x00005648ea2e698b in ram_init_all (rsp=0x5648eb1f0f20 ) > > > > > at ./migration/ram.c:2323 > > > > > #6 0x00005648ea2e6cc5 in ram_save_setup (f=0x5648ec609e00, > > > > > opaque=0x5648eb1f0f20 ) > > > > > at ./migration/ram.c:2436 > > > > > #7 0x00005648ea67b7d3 in qemu_savevm_state_setup (f=0x5648ec609e00) at > > > > > migration/savevm.c:1176 > > > > > #8 0x00005648ea674511 in migration_thread (opaque=0x5648ec031ff0) at > > > > > migration/migration.c:3416 > > > > > #9 0x00005648ea85d65d in qemu_thread_start (args=0x5648ec6057f0) at > > > > > util/qemu-thread-posix.c:519 > > > > > #10 0x00007fb56eac56ba in start_thread () from > > > > > /lib/x86_64-linux-gnu/libpthread.so.0 > > > > > #11 0x00007fb56e7fb41d in clone () from /lib/x86_64-linux-gnu/libc.so.6 > > > > > (gdb) frame 2 > > > > > #2 0x00005648ea376ee6 in vhost_log_global_start > > > > > (listener=0x5648ece4eb08) at ./hw/virtio/vhost.c:857 > > > > > 857 abort(); > > > > > (gdb) list > > > > > 852 { > > > > > 853 int r; > > > > > 854 > > > > > 855 r = vhost_migration_log(listener, true); > > > > > 856 if (r < 0) { > > > > > 857 abort(); > > > > > 858 } > > > > > 859 } > > > > > 860 > > > > > 861 static void vhost_log_global_stop(MemoryListener *listener) > > > > >Since bh postphone the clean up, we can't use the ->started field. > > > > >Do we have any mechanism to get the device type/state in the common > > > > >vhost_migration_log() routine? So for example for the vhost-user/disconnect > > > > >device we will be able to return 0. Or should we implement it and introduce > > > > >it in this patch set? > > > > > > > > > > > > This requires more thought, I will reply in Feng's mail. > > > Okay, let's continue discussion there. > > > > > > No other comments mixed in below. > > > > > > Thanks, Dima. > > > > > > > > > > > Thanks > > > > > > > > > > > > > > > > > >Thanks, Dima. > > > > > > > > > >>Thank > > > > >> > > > > >> > > > > >>> - vhost-user command returns error back to the _start() routine > > > > >>> - Rollback in one place in the start() routine, by calling this > > > > >>> postphoned clean up for the disconnect > > > > >>> > > > > > > > > > -- > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK