Re: [PATCH v3] PCI: hv: Warn when wait_for_response() waits indefinitely

[Wei Liu <wei.liu@kernel.org>]

On Fri, Sep 11, 2026 at 12:29:05PM +0200, Manivannan Sadhasivam wrote:
> On Wed, Sep 09, 2026 at 03:01:22PM +0530, Naman Jain wrote:
> > 
> > 
> > On 9/8/2026 5:00 PM, Sahil Chandna wrote:
> > > A guest can wait indefinitely in wait_for_response() for the host to
> > > send either a rescind message or a packet completion. If the
> > > host does not send either, the guest can remain blocked with no
> > > diagnostic indicating a reason.
> > > This was observed during a guest kernel upgrade in which the
> > > host-side application handling the PCI channel faulted, causing the
> > > guest to never receive the completion request.
> > > Add a warning in wait_for_response() when the wait exceeds
> > > a timeout so that such a hang is visible in the guest's kernel log
> > > and can be correlated with host-side state.
> > > 
> > > Suggested-by: Michael Kelley <mhklinux@outlook.com>
> > > Signed-off-by: Sahil Chandna <sahilchandna@linux.microsoft.com>
> > > ---
> > > Changes since v2:
> > > - Add counter based timeout instead of introducing another timer
> > > Link to v2: https://lore.kernel.org/all/20260902115854.2629164-1-sahilchandna@linux.microsoft.com/
> > > 
> > > Changes since v1:
> > > - Removed periodic warning to one time warning in 2 minutes
> > > - Include vmbus relid and stuck PCI msg.
> > > Link to v1: https://lore.kernel.org/all/20260825051850.2438816-1-sahilchandna@linux.microsoft.com/
> > >   drivers/pci/controller/pci-hyperv.c | 46 ++++++++++++++++++++++-------
> > >   1 file changed, 36 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > > index 89816a2bd7cd..bd07402c47ed 100644
> > > --- a/drivers/pci/controller/pci-hyperv.c
> > > +++ b/drivers/pci/controller/pci-hyperv.c
> > > @@ -1040,19 +1040,38 @@ static void put_pcichild(struct hv_pci_dev *hpdev)
> > > 
> > >   /*
> > >    * There is no good way to get notified from vmbus_onoffer_rescind(),
> > > - * so let's use polling here, since this is not a hot path.
> > > + * so let's use polling here, since this is not a hot path. If
> > > + * wait_for_response() has been polling for 2 minutes
> > > + * without either a rescind or completion, add a warning.
> > >    */
> > > +#define PCI_RESPONSE_HANG_TICKS 1200
> > > +
> > 
> > Nit, I think this variable name could be misleading, as this represents a
> > loop counter for a retry logic, but not exactly *ticks* from kernel
> > terminology.
> > 
> > I would have preferred something like: PCI_RESPONSE_WARN_POLL_COUNT.
> > 
> 
> PCI_RESPONSE_POLL_COUNT?

Sahil, let me know if you will send out another version. If it is only
changing one macro name, I can do that.

Wei