Re: [PATCH v4 1/2] uio_hv_generic: Fix sysfs creation path for ring buffer

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Apr 15, 2025 at 09:24:16PM +0530, Naman Jain wrote:
> 
> 
> On 4/15/2025 8:40 PM, Greg Kroah-Hartman wrote:
> > On Thu, Apr 10, 2025 at 11:38:46AM +0530, Naman Jain wrote:
> > > On regular bootup, devices get registered to VMBus first, so when
> > > uio_hv_generic driver for a particular device type is probed,
> > > the device is already initialized and added, so sysfs creation in
> > > uio_hv_generic probe works fine. However, when device is removed
> > > and brought back, the channel rescinds and device again gets
> > > registered to VMBus. However this time, the uio_hv_generic driver is
> > > already registered to probe for that device and in this case sysfs
> > > creation is tried before the device's kobject gets initialized
> > > completely.
> > > 
> > > Fix this by moving the core logic of sysfs creation for ring buffer,
> > > from uio_hv_generic to HyperV's VMBus driver, where rest of the sysfs
> > > attributes for the channels are defined. While doing that, make use
> > > of attribute groups and macros, instead of creating sysfs directly,
> > > to ensure better error handling and code flow.
> > > 
> > > Problem path:
> > > vmbus_process_offer (new offer comes for the VMBus device)
> > >    vmbus_add_channel_work
> > >      vmbus_device_register
> > >        |-> device_register
> > >        |     |...
> > >        |     |-> hv_uio_probe
> > >        |           |...
> > >        |           |-> sysfs_create_bin_file (leads to a warning as
> > >        |                 primary channel's kobject, which is used to
> > >        |                 create sysfs is not yet initialized)
> > >        |-> kset_create_and_add
> > >        |-> vmbus_add_channel_kobj (initialization of primary channel's
> > >                                    kobject happens later)
> > > 
> > > Above code flow is sequential and the warning is always reproducible in
> > > this path.
> > > 
> > > Fixes: 9ab877a6ccf8 ("uio_hv_generic: make ring buffer attribute for primary channel")
> > > Cc: stable@kernel.org
> > > Suggested-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> > > Suggested-by: Michael Kelley <mhklinux@outlook.com>
> > > Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
> > > ---
> > >   drivers/hv/hyperv_vmbus.h    |   6 ++
> > >   drivers/hv/vmbus_drv.c       | 110 ++++++++++++++++++++++++++++++++++-
> > >   drivers/uio/uio_hv_generic.c |  39 ++++++-------
> > >   include/linux/hyperv.h       |   6 ++
> > >   4 files changed, 138 insertions(+), 23 deletions(-)
> > 
> > Always run checkpatch on a patch before submitting it for review :(
> > 
> 
> Hi Greg,
> I verified again and I could not see checkpatch warnings with patch 1,2.
> There was a warning regarding length of characters for link to previous
> versions in the cover letter but I ignored it.
> 
> I tried on latest linux-next tip with this series fetched from lore using
> b4. I'm sorry, if I am missing something, but can you please try again.

I've pointed out the first thing that I noticed, thanks.