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From: Eric Farman <farman@linux.ibm.com>
To: Cornelia Huck <cohuck@redhat.com>,
	Matthew Rosato <mjrosato@linux.ibm.com>,
	Halil Pasic <pasic@linux.ibm.com>
Cc: Jared Rossi <jrossi@linux.ibm.com>,
	linux-s390@vger.kernel.org, kvm@vger.kernel.org,
	Eric Farman <farman@linux.ibm.com>
Subject: [RFC PATCH v5 3/3] vfio-ccw: Serialize FSM IDLE state with I/O completion
Date: Mon, 10 May 2021 22:56:46 +0200	[thread overview]
Message-ID: <20210510205646.1845844-4-farman@linux.ibm.com> (raw)
In-Reply-To: <20210510205646.1845844-1-farman@linux.ibm.com>

Today, the stacked call to vfio_ccw_sch_io_todo() does three things:

  1) Update a solicited IRB with CP information, and release the CP
     if the interrupt was the end of a START operation.
  2) Copy the IRB data into the io_region, under the protection of
     the io_mutex
  3) Reset the vfio-ccw FSM state to IDLE to acknowledge that
     vfio-ccw can accept more work.

The trouble is that step 3 is (A) invoked for both solicited and
unsolicited interrupts, and (B) sitting after the mutex for step 2.
This second piece becomes a problem if it processes an interrupt
for a CLEAR SUBCHANNEL while another thread initiates a START,
thus allowing the CP and FSM states to get out of sync. That is:

    CPU 1                           CPU 2
    fsm_do_clear()
    fsm_irq()
                                    fsm_io_request()
    vfio_ccw_sch_io_todo()
                                    fsm_io_helper()

Since the FSM state and CP should be kept in sync, let's make a
note when the CP is released, and rely on that as an indication
that the FSM should also be reset at the end of this routine and
open up the device for more work.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 drivers/s390/cio/vfio_ccw_drv.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index 8c625b530035..ef39182edab5 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -85,7 +85,7 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
 {
 	struct vfio_ccw_private *private;
 	struct irb *irb;
-	bool is_final;
+	bool is_final, is_finished = false;
 
 	private = container_of(work, struct vfio_ccw_private, io_work);
 	irb = &private->irb;
@@ -94,14 +94,16 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
 		     (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT));
 	if (scsw_is_solicited(&irb->scsw)) {
 		cp_update_scsw(&private->cp, &irb->scsw);
-		if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING)
+		if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) {
 			cp_free(&private->cp);
+			is_finished = true;
+		}
 	}
 	mutex_lock(&private->io_mutex);
 	memcpy(private->io_region->irb_area, irb, sizeof(*irb));
 	mutex_unlock(&private->io_mutex);
 
-	if (private->mdev && is_final)
+	if (private->mdev && is_finished)
 		private->state = VFIO_CCW_STATE_IDLE;
 
 	if (private->io_trigger)
-- 
2.25.1


  parent reply	other threads:[~2021-05-10 20:56 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10 20:56 [RFC PATCH v5 0/3] vfio-ccw: Fix interrupt handling for HALT/CLEAR Eric Farman
2021-05-10 20:56 ` [RFC PATCH v5 1/3] vfio-ccw: Check initialized flag in cp_init() Eric Farman
2021-05-10 20:56 ` [RFC PATCH v5 2/3] vfio-ccw: Reset FSM state to IDLE inside FSM Eric Farman
2021-05-10 20:56 ` Eric Farman [this message]
2021-05-11 11:31   ` [RFC PATCH v5 3/3] vfio-ccw: Serialize FSM IDLE state with I/O completion Cornelia Huck
2021-05-11 18:02     ` Eric Farman

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