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From: "Michael S. Tsirkin" <mst@redhat.com>
To: 谢永吉 <xieyongji@bytedance.com>
Cc: jasowang@redhat.com, akpm@linux-foundation.org,
	linux-mm@kvack.org, virtualization@lists.linux-foundation.org
Subject: Re: [External] Re: [RFC 3/4] vduse: grab the module's references until there is no vduse device
Date: Mon, 19 Oct 2020 12:41:46 -0400	[thread overview]
Message-ID: <20201019123835-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CACycT3vG+ZEhn3SYy=7c5rkMz4XRbQZL21NdpPozPnH_x6Srhg@mail.gmail.com>

On Mon, Oct 19, 2020 at 11:56:35PM +0800, 谢永吉 wrote:
> 
> 
> 
> On Mon, Oct 19, 2020 at 11:47 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> 
>     On Mon, Oct 19, 2020 at 11:44:36PM +0800, 谢永吉 wrote:
>     >
>     >
>     > On Mon, Oct 19, 2020 at 11:05 PM Michael S. Tsirkin <mst@redhat.com>
>     wrote:
>     >
>     >     On Mon, Oct 19, 2020 at 10:56:22PM +0800, Xie Yongji wrote:
>     >     > The module should not be unloaded if any vduse device exists.
>     >     > So increase the module's reference count when creating vduse
>     >     > device. And the reference count is kept until the device is
>     >     > destroyed.
>     >     >
>     >     > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
>     >     > ---
>     >     >  drivers/vdpa/vdpa_user/vduse_dev.c | 2 ++
>     >     >  1 file changed, 2 insertions(+)
>     >     >
>     >     > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/
>     vdpa_user/
>     >     vduse_dev.c
>     >     > index 6787ba66725c..f04aa02de8c1 100644
>     >     > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
>     >     > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
>     >     > @@ -887,6 +887,7 @@ static int vduse_destroy_dev(u32 id)
>     >     >       kfree(dev->vqs);
>     >     >       vduse_iova_domain_destroy(dev->domain);
>     >     >       vduse_dev_destroy(dev);
>     >     > +     module_put(THIS_MODULE);
>     >     > 
>     >     >       return 0;
>     >     >  }
>     >     > @@ -931,6 +932,7 @@ static int vduse_create_dev(struct
>     vduse_dev_config
>     >     *config)
>     >     > 
>     >     >       dev->connected = true;
>     >     >       list_add(&dev->list, &vduse_devs);
>     >     > +     __module_get(THIS_MODULE);
>     >     > 
>     >     >       return fd;
>     >     >  err_fd:
>     >
>     >     This kind of thing is usually an indicator of a bug. E.g.
>     >     if the refcount drops to 0 on module_put(THIS_MODULE) it
>     >     will be unloaded and the following return will not run.
>     >
>     >
>     >
>     > Should this happen?  The refcount should be only decreased to 0 after the
>     > misc_device is closed?
>     >
>     > Thanks,
>     > Yongji
>     >
> 
>     OTOH if it never drops to 0 anyway then why do you need to increase it?
> 
> 
> 
> To prevent unloading the module in the case that the device is created, but no
> user process using it (e.g. the user process crashed). 
> 
> Thanks,
> Yongji

Looks like it can drop to 0 if that is the case then?


> 
>     >
>     >
>     >     > --
>     >     > 2.25.1
>     >
>     >
> 
> 



  reply	other threads:[~2020-10-19 16:42 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-19 14:56 [RFC 0/4] Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2020-10-19 14:56 ` [RFC 1/4] mm: export zap_page_range() for driver use Xie Yongji
2020-10-19 15:14   ` Matthew Wilcox
2020-10-19 15:36     ` [External] " 谢永吉
2020-10-19 14:56 ` [RFC 2/4] vduse: Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2020-10-19 15:08   ` Michael S. Tsirkin
2020-10-19 15:24     ` Randy Dunlap
2020-10-19 15:46       ` [External] " 谢永吉
2020-10-19 15:48     ` 谢永吉
2020-10-19 14:56 ` [RFC 3/4] vduse: grab the module's references until there is no vduse device Xie Yongji
2020-10-19 15:05   ` Michael S. Tsirkin
2020-10-19 15:44     ` [External] " 谢永吉
2020-10-19 15:47       ` Michael S. Tsirkin
2020-10-19 15:56         ` 谢永吉
2020-10-19 16:41           ` Michael S. Tsirkin [this message]
2020-10-20  7:42             ` Yongji Xie
2020-10-19 14:56 ` [RFC 4/4] vduse: Add memory shrinker to reclaim bounce pages Xie Yongji
2020-10-19 17:16 ` [RFC 0/4] Introduce VDUSE - vDPA Device in Userspace Michael S. Tsirkin
2020-10-20  2:18   ` [External] " 谢永吉
2020-10-20  2:20     ` Jason Wang
2020-10-20  2:28       ` 谢永吉
2020-10-20  3:20 ` Jason Wang
2020-10-20  7:39   ` [External] " Yongji Xie
2020-10-20  8:01     ` Jason Wang
2020-10-20  8:35       ` Yongji Xie
2020-10-20  9:12         ` Jason Wang
2020-10-23  2:55           ` Yongji Xie
2020-10-23  8:44             ` Jason Wang

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