From: Cornelia Huck <cohuck@redhat.com>
To: Eric Farman <farman@linux.ibm.com>
Cc: Jared Rossi <jrossi@linux.ibm.com>,
Halil Pasic <pasic@linux.ibm.com>,
linux-s390@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [RFC PATCH v3 3/3] vfio-ccw: Check workqueue before doing START
Date: Fri, 19 Jun 2020 13:40:05 +0200 [thread overview]
Message-ID: <20200619134005.512fc54f.cohuck@redhat.com> (raw)
In-Reply-To: <20200616195053.99253-4-farman@linux.ibm.com>
On Tue, 16 Jun 2020 21:50:53 +0200
Eric Farman <farman@linux.ibm.com> wrote:
> When an interrupt is received via the IRQ, the bulk of the work is
> stacked on a workqueue for later processing. Which means that concurrent
> START or a HALT/CLEAR operation (via the async_region) will race with
> this process and require some serialization.
>
> Once we have all our locks acquired, let's just look to see if we're
> in a window where the process has been started from the IRQ, but not
> yet picked up by vfio-ccw to clean up an I/O. If there is, mark the
> request as BUSY so it can be redriven after we have a chance to breathe.
This change looks reasonable to me. It would be even better if we could
send off I/O requests at any time; but if signaling to retry saves us
from some hairy code elsewhere, it is a good idea to do so.
>
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
> drivers/s390/cio/vfio_ccw_fsm.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
> index f0952192480e..9dc5b4d549b3 100644
> --- a/drivers/s390/cio/vfio_ccw_fsm.c
> +++ b/drivers/s390/cio/vfio_ccw_fsm.c
> @@ -28,6 +28,11 @@ static int fsm_io_helper(struct vfio_ccw_private *private)
>
> spin_lock_irqsave(sch->lock, flags);
>
> + if (work_pending(&private->io_work)) {
> + ret = -EBUSY;
> + goto out;
> + }
> +
> orb = cp_get_orb(&private->cp, (u32)(addr_t)sch, sch->lpm);
> if (!orb) {
> ret = -EIO;
next prev parent reply other threads:[~2020-06-19 11:40 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-16 19:50 [RFC PATCH v3 0/3] vfio-ccw: Fix interrupt handling for HALT/CLEAR Eric Farman
2020-06-16 19:50 ` [RFC PATCH v3 1/3] vfio-ccw: Indicate if a channel_program is started Eric Farman
2020-06-17 23:11 ` Halil Pasic
2020-06-18 11:47 ` Eric Farman
2020-06-16 19:50 ` [RFC PATCH v3 2/3] vfio-ccw: Remove the CP_PENDING FSM state Eric Farman
2020-06-16 19:50 ` [RFC PATCH v3 3/3] vfio-ccw: Check workqueue before doing START Eric Farman
2020-06-19 11:40 ` Cornelia Huck [this message]
2020-06-17 11:24 ` [RFC PATCH v3 0/3] vfio-ccw: Fix interrupt handling for HALT/CLEAR Eric Farman
2020-06-29 14:56 ` Cornelia Huck
2020-06-30 19:10 ` Eric Farman
2020-06-19 11:21 ` Cornelia Huck
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