linux-kernel - Re: [PATCH v3] virtio_console: allocate inbufs in add

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Message-ID: <108357faa8d7add057a8dc0870b42c482eec34ee.camel@infradead.org>
Date:   Wed, 04 Dec 2019 14:58:51 +0100
From:   Amit Shah <amit@...radead.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Laurent Vivier <lvivier@...hat.com>, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, stable@...r.kernel.org
Subject: Re: [PATCH v3] virtio_console: allocate inbufs in add_port() only
 if it is needed

On Tue, 2019-12-03 at 10:42 -0500, Michael S. Tsirkin wrote:
> On Tue, Dec 03, 2019 at 03:46:50PM +0100, Amit Shah wrote:
> > On Thu, 2019-11-14 at 13:25 +0100, Laurent Vivier wrote:
> > > When we hot unplug a virtserialport and then try to hot plug
> > > again,
> > > it fails:
> > > 
> > > (qemu) chardev-add
> > > socket,id=serial0,path=/tmp/serial0,server,nowait
> > > (qemu) device_add virtserialport,bus=virtio-serial0.0,nr=2,\
> > >                   chardev=serial0,id=serial0,name=serial0
> > > (qemu) device_del serial0
> > > (qemu) device_add virtserialport,bus=virtio-serial0.0,nr=2,\
> > >                   chardev=serial0,id=serial0,name=serial0
> > > kernel error:
> > >   virtio-ports vport2p2: Error allocating inbufs
> > > qemu error:
> > >   virtio-serial-bus: Guest failure in adding port 2 for device \
> > >                      virtio-serial0.0
> > > 
> > > This happens because buffers for the in_vq are allocated when the
> > > port is
> > > added but are not released when the port is unplugged.
> > > 
> > > They are only released when virtconsole is removed (see
> > > a7a69ec0d8e4)
> > > 
> > > To avoid the problem and to be symmetric, we could allocate all
> > > the
> > > buffers
> > > in init_vqs() as they are released in remove_vqs(), but it sounds
> > > like
> > > a waste of memory.
> > > 
> > > Rather than that, this patch changes add_port() logic to ignore
> > > ENOSPC
> > > error in fill_queue(), which means queue has already been filled.
> > > 
> > > Fixes: a7a69ec0d8e4 ("virtio_console: free buffers after reset")
> > > Cc: mst@...hat.com
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Laurent Vivier <lvivier@...hat.com>
> > 
> > Reviewed-by: Amit Shah <amit@...nel.org>
> > 
> > Thanks!
> 
> 
> Thanks, however this has already been merged by Linus.
> I can't add the tag retroactively, sorry about that.

Right, no problem - but I wanted to ensure it's on-list :)

> 
> For bugfix patches like that, I think we can reasonably
> target a turn around of a couple of days, these
> shouldn't really need to wait weeks for review.

Sure, thanks for picking it up fast enough.  Life happens, etc., and
it's not always possible to reply in a couple of days.  Since we had
already covered the main comments in v1 and v2, v3 wasn't going to need
much attention anyway.