On Tue, 11 May 2021 21:56:31 +0200 Eric Farman <farman@xxxxxxxxxxxxx> wrote: > 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@xxxxxxxxxxxxx> > --- > drivers/s390/cio/vfio_ccw_drv.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) Looking good :) Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
