[RFC v1 1/1] vfio-ccw: Don't call cp_free if we are processing a channel program

Farhan Ali
2019-06-20T21:17:24Z

There is a small window where it's possible that an interrupt can
arrive and can call cp_free, while we are still processing a channel
program (i.e allocating memory, pinnging pages, translating
addresses etc). This can lead to allocating and freeing at the same
time and can cause memory corruption.

Let's not call cp_free if we are currently processing a channel program.

Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
---

I have been running my test overnight with this patch and I haven't
seen the stack traces that I mentioned about earlier. I would like
to get some reviews on this and also if this is the right thing to
do?

Thanks
Farhan

drivers/s390/cio/vfio_ccw_drv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index 66a66ac..61ece3f 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -88,7 +88,7 @@ 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)
+ if (is_final && private->state != VFIO_CCW_STATE_CP_PROCESSING)
cp_free(&private->cp);
}
mutex_lock(&private->io_mutex);
--
2.7.4