Re: [PATCH v2 5/5] vhost: add device started check in migration set log

[Michael S. Tsirkin]

On Fri, May 15, 2020 at 07:54:57PM +0300, 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?

Either works I think.

> 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 <ram_state>)
>       at ./migration/ram.c:2323
>   #6  0x00005648ea2e6cc5 in ram_save_setup (f=0x5648ec609e00,
>       opaque=0x5648eb1f0f20 <ram_state>)
>       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?
> 
> 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
> > >
> >