Re: [PATCH 4/4] vfio: ccw: add traceponits for interesting error paths

Cornelia Huck
2018-03-26T13:59:02Z

On Wed, 21 Mar 2018 03:08:22 +0100
Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com> wrote:

> From: Halil Pasic <pasic@linux.vnet.ibm.com>
>
> Add some tracepoints so we can inspect what is not working as is should.

Tracepoints are certainly helpful (we can add more later).

>
> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
> Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
> ---
> drivers/s390/cio/Makefile | 1 +
> drivers/s390/cio/vfio_ccw_fsm.c | 13 ++++++
> drivers/s390/cio/vfio_ccw_trace.h | 86 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 100 insertions(+)
> create mode 100644 drivers/s390/cio/vfio_ccw_trace.h
>
> diff --git a/drivers/s390/cio/Makefile b/drivers/s390/cio/Makefile
> index a070ef0efe65..f230516abb96 100644
> --- a/drivers/s390/cio/Makefile
> +++ b/drivers/s390/cio/Makefile
> @@ -5,6 +5,7 @@
>
> # The following is required for define_trace.h to find ./trace.h
> CFLAGS_trace.o := -I$(src)
> +CFLAGS_vfio_ccw_fsm.o := -I$(src)
>
> obj-y += airq.o blacklist.o chsc.o cio.o css.o chp.o idset.o isc.o \
> fcx.o itcw.o crw.o ccwreq.o trace.o ioasm.o
> diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
> index c30420c517b1..7ed27f90d741 100644
> --- a/drivers/s390/cio/vfio_ccw_fsm.c
> +++ b/drivers/s390/cio/vfio_ccw_fsm.c
> @@ -13,6 +13,9 @@
> #include "ioasm.h"
> #include "vfio_ccw_private.h"
>
> +#define CREATE_TRACE_POINTS
> +#include "vfio_ccw_trace.h"
> +
> static int fsm_io_helper(struct vfio_ccw_private *private)
> {
> struct subchannel *sch;
> @@ -105,6 +108,10 @@ static void fsm_disabled_irq(struct vfio_ccw_private *private,
> */
> cio_disable_subchannel(sch);
> }
> +inline struct subchannel_id get_schid(struct vfio_ccw_private *p)
> +{
> + return p->sch->schid;
> +}
>
> /*
> * Deal with the ccw command request from the userspace.
> @@ -131,6 +138,8 @@ static void fsm_io_request(struct vfio_ccw_private *private,
>
> io_region->ret_code = cp_prefetch(&private->cp);
> if (io_region->ret_code) {
> + trace_vfio_ccw_cp_prefetch_failed(get_schid(private),
> + io_region->ret_code);
> cp_free(&private->cp);
> goto err_out;
> }
> @@ -138,6 +147,8 @@ static void fsm_io_request(struct vfio_ccw_private *private,
> /* Start channel program and wait for I/O interrupt. */
> io_region->ret_code = fsm_io_helper(private);
> if (io_region->ret_code) {
> + trace_vfio_ccw_ssch_failed(get_schid(private),
> + io_region->ret_code);
> cp_free(&private->cp);
> goto err_out;
> }
> @@ -145,10 +156,12 @@ static void fsm_io_request(struct vfio_ccw_private *private,
> } else if (scsw->cmd.fctl & SCSW_FCTL_HALT_FUNC) {
> /* XXX: Handle halt. */
> io_region->ret_code = -EOPNOTSUPP;
> + trace_vfio_ccw_halt(get_schid(private));
> goto err_out;
> } else if (scsw->cmd.fctl & SCSW_FCTL_CLEAR_FUNC) {
> /* XXX: Handle clear. */
> io_region->ret_code = -EOPNOTSUPP;
> + trace_vfio_ccw_clear(get_schid(private));
> goto err_out;

Hmmm.... perhaps better to just trace the function (start/halt/clear)
in any case?

> }
>
> diff --git a/drivers/s390/cio/vfio_ccw_trace.h b/drivers/s390/cio/vfio_ccw_trace.h
> new file mode 100644
> index 000000000000..edd3321cd919
> --- /dev/null
> +++ b/drivers/s390/cio/vfio_ccw_trace.h
> @@ -0,0 +1,86 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + * Tracepoints for vfio_ccw driver
> + *
> + * Copyright IBM Corp. 2018
> + *
> + * Author(s): Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
> + * Halil Pasic <pasic@linux.vnet.ibm.com>
> + */
> +
> +
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM vfio_ccw
> +
> +#if !defined(_VFIO_CCW_TRACE_) || defined(TRACE_HEADER_MULTI_READ)
> +#define _VFIO_CCW_TRACE_
> +
> +#include <linux/tracepoint.h>
> +
> +TRACE_EVENT(vfio_ccw_cp_prefetch_failed,
> + TP_PROTO(struct subchannel_id schid, int errno),
> + TP_ARGS(schid, errno),
> +
> + TP_STRUCT__entry(
> + __field_struct(struct subchannel_id, schid)
> + __field(int, errno)
> + ),
> +
> + TP_fast_assign(
> + __entry->schid = schid;
> + __entry->errno = errno;
> + ),
> +
> + TP_printk("(schid 0.%x.%04X) translation failed (errno: %d)",
> + __entry->schid.ssid, __entry->schid.sch_no, __entry->errno)
> +);
> +
> +TRACE_EVENT(vfio_ccw_ssch_failed,
> + TP_PROTO(struct subchannel_id schid, int errno),
> + TP_ARGS(schid, errno),
> +
> + TP_STRUCT__entry(
> + __field_struct(struct subchannel_id, schid)
> + __field(int, errno)
> + ),
> +
> + TP_fast_assign(
> + __entry->schid = schid;
> + __entry->errno = errno;
> + ),
> +
> + TP_printk("(schid 0.%x.%04X) ssch failed (errno: %d)",
> + __entry->schid.ssid, __entry->schid.sch_no, __entry->errno)
> +);
> +
> +DECLARE_EVENT_CLASS(vfio_ccw_notsupp,
> + TP_PROTO(struct subchannel_id schid),
> + TP_ARGS(schid),
> +
> + TP_STRUCT__entry(
> + __field_struct(struct subchannel_id, schid)
> + ),
> +
> + TP_fast_assign(
> + __entry->schid = schid;
> + ),
> +
> + TP_printk("(schid 0.%x.%04X) request not supported",
> + __entry->schid.ssid, __entry->schid.sch_no)
> +);

Especially as I don't plan to leave this unsupported for too long :)

Just tracing the function is useful now and will stay useful in the
future.

Another idea: Trace the fsm state transitions. Probably something for
an additional patch.

> +
> +DEFINE_EVENT(vfio_ccw_notsupp, vfio_ccw_clear,
> + TP_PROTO(struct subchannel_id schid), TP_ARGS(schid));
> +
> +DEFINE_EVENT(vfio_ccw_notsupp, vfio_ccw_halt,
> + TP_PROTO(struct subchannel_id schid), TP_ARGS(schid));
> +
> +#endif /* _VFIO_CCW_TRACE_ */
> +
> +/* This part must be outside protection */
> +
> +#undef TRACE_INCLUDE_PATH
> +#define TRACE_INCLUDE_PATH .
> +#undef TRACE_INCLUDE_FILE
> +#define TRACE_INCLUDE_FILE vfio_ccw_trace
> +
> +#include <trace/define_trace.h>