Re: [PATCH v3 1/1] vfio-ccw: Prevent quiesce function going into an infinite loop

Cornelia Huck
2019-04-24T16:35:12Z

On Tue, 16 Apr 2019 17:23:14 -0400
Farhan Ali <alifm@linux.ibm.com> wrote:

> The quiesce function calls cio_cancel_halt_clear() and if we
> get an -EBUSY we go into a loop where we:
> - wait for any interrupts
> - flush all I/O in the workqueue
> - retry cio_cancel_halt_clear
>
> During the period where we are waiting for interrupts or
> flushing all I/O, the channel subsystem could have completed
> a halt/clear action and turned off the corresponding activity
> control bits in the subchannel status word. This means the next
> time we call cio_cancel_halt_clear(), we will again start by
> calling cancel subchannel and so we can be stuck between calling
> cancel and halt forever.
>
> Rather than calling cio_cancel_halt_clear() immediately after
> waiting, let's try to disable the subchannel. If we succeed in
> disabling the subchannel then we know nothing else can happen
> with the device.
>
> Suggested-by: Eric Farman <farman@linux.ibm.com>
> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> ---
> ChangeLog:
> v2 -> v3
> - Log an error message when cio_cancel_halt_clear
> returns EIO and break out of the loop.
>
> - Did not include past change log as the other patches
> of the original series have been queued by Conny.
> Old series (v2) can be found here:
> https://marc.info/?l=kvm&m=155475754101769&w=2
>
> drivers/s390/cio/vfio_ccw_drv.c | 32 ++++++++++++++++++--------------
> 1 file changed, 18 insertions(+), 14 deletions(-)

Thanks, applied.