Linux Virtualization - Sep 2016 - [PATCH] virtio-blk: Generate uevent after attribute available

On Tue, 06/28 04:45, Christoph Hellwig wrote:
> On Tue, Jun 28, 2016 at 10:39:15AM +0800, Fam Zheng wrote:
> > Userspace listens to the KOBJ_ADD uevent generated in add_disk. At
that
> > point we haven't created the serial attribute file, therefore
depending
> > on how fast udev reacts, the /dev/disk/by-id/ entry doesn't always
get
> > created.
> > 
> > This race condition can be easily reproduced by hot plugging a number
of
> > virtio-blk disks.
> > 
> > Also in systemd, there used to be a related workaround in udev rules
> > called 'WAIT_FOR="serial"', but it is removed in
later versions.
> > 
> > Now let's generate a KOBJ_CHANGE event after the attributes are
ready.
> 
> The same race is present in other drivers as well, e.g. nvme.  Please
> find a way to make this work properly without needing to hack every
> driver to send events manually.
OK, I'll take a look today!

Fam

On Wed, Jun 29, 2016 at 09:24:15AM +0800, Fam Zheng
wrote:
> On Tue, 06/28 04:45, Christoph Hellwig wrote:
> > On Tue, Jun 28, 2016 at 10:39:15AM +0800, Fam Zheng wrote:
> > > Userspace listens to the KOBJ_ADD uevent generated in add_disk.
At that
> > > point we haven't created the serial attribute file, therefore
depending
> > > on how fast udev reacts, the /dev/disk/by-id/ entry doesn't
always get
> > > created.
> > > 
> > > This race condition can be easily reproduced by hot plugging a
number of
> > > virtio-blk disks.
> > > 
> > > Also in systemd, there used to be a related workaround in udev
rules
> > > called 'WAIT_FOR="serial"', but it is removed
in later versions.
> > > 
> > > Now let's generate a KOBJ_CHANGE event after the attributes
are ready.
> > 
> > The same race is present in other drivers as well, e.g. nvme.  Please
> > find a way to make this work properly without needing to hack every
> > driver to send events manually.
> 
> OK, I'll take a look today!
> 
> Fam
Was this fixed in the generic code?

-- 
MST

On Sat, 09/03 01:56, Michael S. Tsirkin wrote:
> On Wed, Jun 29, 2016 at 09:24:15AM +0800, Fam Zheng wrote:
> > On Tue, 06/28 04:45, Christoph Hellwig wrote:
> > > On Tue, Jun 28, 2016 at 10:39:15AM +0800, Fam Zheng wrote:
> > > > Userspace listens to the KOBJ_ADD uevent generated in
add_disk. At that
> > > > point we haven't created the serial attribute file,
therefore depending
> > > > on how fast udev reacts, the /dev/disk/by-id/ entry
doesn't always get
> > > > created.
> > > > 
> > > > This race condition can be easily reproduced by hot plugging
a number of
> > > > virtio-blk disks.
> > > > 
> > > > Also in systemd, there used to be a related workaround in
udev rules
> > > > called 'WAIT_FOR="serial"', but it is
removed in later versions.
> > > > 
> > > > Now let's generate a KOBJ_CHANGE event after the
attributes are ready.
> > > 
> > > The same race is present in other drivers as well, e.g. nvme. 
Please
> > > find a way to make this work properly without needing to hack
every
> > > driver to send events manually.
> > 
> > OK, I'll take a look today!
> > 
> > Fam
> 
> Was this fixed in the generic code?
A proposed fix is:

https://lkml.org/lkml/2016/8/17/81

Fam