hotplug issue of vhost-user-blk

hotplug issue of vhost-user-blk

[Li Feng]

Hi all,

Hotplug of vhost-user-blk doesn't not work in qemu master branch and
all previous version.

The action I insert a vhost-user-blk disk is:
(qemu) chardev-add socket,id=spdk_vhost_blk2,path=/vhost-blk.0,reconnect=1
(qemu) device_add
vhost-user-blk-pci,chardev=spdk_vhost_blk2,id=spdk_vhost_blk2,num-queues=4

Until here, it's well.

Then I unplug it from qemu:
(qemu) device_del spdk_vhost_blk2
(qemu) chardev-remove spdk_vhost_blk2
Error: Chardev 'spdk_vhost_blk2' is busy

The related code is here:
qmp_chardev_remove
    -> qemu_chr_is_busy
    -> object_unparent(OBJECT(chr));

 330 static bool qemu_chr_is_busy(Chardev *s)
 331 {
 332     if (CHARDEV_IS_MUX(s)) {
 333         MuxChardev *d = MUX_CHARDEV(s);
 334         return d->mux_cnt >= 0;
 335     } else {
 336         return s->be != NULL;
 337     }
 338 }

My question is:
1. s->be is set to NULL when qemu_chr_fe_deinit is called.
However, the qmp_chardev_remove is blocked at qemu_chr_is_busy check,
then the object_unparent will not be called.
2. Is there a path that device_del will trigger the s->be that been set to NULL?

How should I fix this issue?
I have tested that comment the qemu_chr_is_busy works well.

Thanks in advance.

Feng Li

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Re: hotplug issue of vhost-user-blk

[Igor Mammedov]

On Wed, 8 Apr 2020 10:25:42 +0800
Li Feng <fengli@smartx.com> wrote:

> Hi all,
> 
> Hotplug of vhost-user-blk doesn't not work in qemu master branch and
> all previous version.
> 
> The action I insert a vhost-user-blk disk is:
> (qemu) chardev-add socket,id=spdk_vhost_blk2,path=/vhost-blk.0,reconnect=1
> (qemu) device_add
> vhost-user-blk-pci,chardev=spdk_vhost_blk2,id=spdk_vhost_blk2,num-queues=4
> 
> Until here, it's well.
> 
> Then I unplug it from qemu:
> (qemu) device_del spdk_vhost_blk2
> (qemu) chardev-remove spdk_vhost_blk2
> Error: Chardev 'spdk_vhost_blk2' is busy
> 
> The related code is here:
> qmp_chardev_remove
>     -> qemu_chr_is_busy
>     -> object_unparent(OBJECT(chr));  
> 
>  330 static bool qemu_chr_is_busy(Chardev *s)
>  331 {
>  332     if (CHARDEV_IS_MUX(s)) {
>  333         MuxChardev *d = MUX_CHARDEV(s);
>  334         return d->mux_cnt >= 0;
>  335     } else {
>  336         return s->be != NULL;
>  337     }
>  338 }
> 
> My question is:
> 1. s->be is set to NULL when qemu_chr_fe_deinit is called.
> However, the qmp_chardev_remove is blocked at qemu_chr_is_busy check,
> then the object_unparent will not be called.
> 2. Is there a path that device_del will trigger the s->be that been set to NULL?

device_del is request for guest to eject device and once it's done backend
could be removed. 

what's you command line? (so I could point out entry point where ejection happens
for you to troubleshoot it further)

> 
> How should I fix this issue?
> I have tested that comment the qemu_chr_is_busy works well.
> 
> Thanks in advance.
> 
> Feng Li
> 

Re: hotplug issue of vhost-user-blk

[Li Feng]

Thanks!
After waiting some seconds after device_del:
(qemu) device_del spdk_vhost_blk2
sleep 5
(qemu) chardev-remove spdk_vhost_blk2
Error: Chardev 'spdk_vhost_blk2' is busy

It works. However, I find some crashes about the vhost-user-blk.
I will send out the patches after all tests.

Thanks,

Feng Li

Igor Mammedov <imammedo@redhat.com> 于2020年4月8日周三 下午6:40写道：
>
> On Wed, 8 Apr 2020 10:25:42 +0800
> Li Feng <fengli@smartx.com> wrote:
>
> > Hi all,
> >
> > Hotplug of vhost-user-blk doesn't not work in qemu master branch and
> > all previous version.
> >
> > The action I insert a vhost-user-blk disk is:
> > (qemu) chardev-add socket,id=spdk_vhost_blk2,path=/vhost-blk.0,reconnect=1
> > (qemu) device_add
> > vhost-user-blk-pci,chardev=spdk_vhost_blk2,id=spdk_vhost_blk2,num-queues=4
> >
> > Until here, it's well.
> >
> > Then I unplug it from qemu:
> > (qemu) device_del spdk_vhost_blk2
> > (qemu) chardev-remove spdk_vhost_blk2
> > Error: Chardev 'spdk_vhost_blk2' is busy
> >
> > The related code is here:
> > qmp_chardev_remove
> >     -> qemu_chr_is_busy
> >     -> object_unparent(OBJECT(chr));
> >
> >  330 static bool qemu_chr_is_busy(Chardev *s)
> >  331 {
> >  332     if (CHARDEV_IS_MUX(s)) {
> >  333         MuxChardev *d = MUX_CHARDEV(s);
> >  334         return d->mux_cnt >= 0;
> >  335     } else {
> >  336         return s->be != NULL;
> >  337     }
> >  338 }
> >
> > My question is:
> > 1. s->be is set to NULL when qemu_chr_fe_deinit is called.
> > However, the qmp_chardev_remove is blocked at qemu_chr_is_busy check,
> > then the object_unparent will not be called.
> > 2. Is there a path that device_del will trigger the s->be that been set to NULL?
>
> device_del is request for guest to eject device and once it's done backend
> could be removed.
>
> what's you command line? (so I could point out entry point where ejection happens
> for you to troubleshoot it further)
>
> >
> > How should I fix this issue?
> > I have tested that comment the qemu_chr_is_busy works well.
> >
> > Thanks in advance.
> >
> > Feng Li
> >
>

-- 
The SmartX email address is only for business purpose. Any sent message 
that is not related to the business is not authorized or permitted by 
SmartX.
本邮箱为北京志凌海纳科技有限公司（SmartX）工作邮箱. 如本邮箱发出的邮件与工作无关,该邮件未得到本公司任何的明示或默示的授权.

Re: hotplug issue of vhost-user-blk

[Michael S. Tsirkin]

On Wed, Apr 08, 2020 at 10:25:42AM +0800, Li Feng wrote:
> Hi all,
> 
> Hotplug of vhost-user-blk doesn't not work in qemu master branch and
> all previous version.
> 
> The action I insert a vhost-user-blk disk is:
> (qemu) chardev-add socket,id=spdk_vhost_blk2,path=/vhost-blk.0,reconnect=1
> (qemu) device_add
> vhost-user-blk-pci,chardev=spdk_vhost_blk2,id=spdk_vhost_blk2,num-queues=4
> 
> Until here, it's well.
> 
> Then I unplug it from qemu:
> (qemu) device_del spdk_vhost_blk2
> (qemu) chardev-remove spdk_vhost_blk2
> Error: Chardev 'spdk_vhost_blk2' is busy

Pan Nengyuan (cc'd) fixed unplug recently so I expect it
worked for him after the patch ...

> The related code is here:
> qmp_chardev_remove
>     -> qemu_chr_is_busy
>     -> object_unparent(OBJECT(chr));
> 
>  330 static bool qemu_chr_is_busy(Chardev *s)
>  331 {
>  332     if (CHARDEV_IS_MUX(s)) {
>  333         MuxChardev *d = MUX_CHARDEV(s);
>  334         return d->mux_cnt >= 0;
>  335     } else {
>  336         return s->be != NULL;
>  337     }
>  338 }
> 
> My question is:
> 1. s->be is set to NULL when qemu_chr_fe_deinit is called.
> However, the qmp_chardev_remove is blocked at qemu_chr_is_busy check,
> then the object_unparent will not be called.
> 2. Is there a path that device_del will trigger the s->be that been set to NULL?
> 
> How should I fix this issue?
> I have tested that comment the qemu_chr_is_busy works well.
> 
> Thanks in advance.
> 
> Feng Li
> 
> -- 
> The SmartX email address is only for business purpose. Any sent message 
> that is not related to the business is not authorized or permitted by 
> SmartX.
> 本邮箱为北京志凌海纳科技有限公司（SmartX）工作邮箱. 如本邮箱发出的邮件与工作无关,该邮件未得到本公司任何的明示或默示的授权.
>