Quoting Chris Wilson (2018-03-30 14:18:01)
> We don't handle resetting the kernel context very well, or presumably any
> context executing its breadcrumb commands in the ring as opposed to the
> batchbuffer and flush. If we trigger a device reset twice in quick
> succession while the kernel context is executing, we may end up skipping
> the breadcrumb. This is really only a problem for the selftest as
> normally there is a large interlude between resets (hangcheck), or we
> focus on resetting just one engine and so avoid repeatedly resetting
> innocents.
>
> Something to try would be a preempt-to-idle to quiesce the engine before
> reset, so that innocent contexts would be spared the reset.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> CC: Michel Thierry <michel.thierry@xxxxxxxxx>
Anyone?
> ---
> drivers/gpu/drm/i915/i915_drv.c | 3 ++
> drivers/gpu/drm/i915/selftests/intel_hangcheck.c | 48 ++++++++++++++++++++++--
> 2 files changed, 47 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index d354627882e3..684060ed8db6 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -1886,6 +1886,8 @@ void i915_reset(struct drm_i915_private *i915)
> int ret;
> int i;
>
> + GEM_TRACE("flags=%lx\n", error->flags);
> +
> might_sleep();
> lockdep_assert_held(&i915->drm.struct_mutex);
> GEM_BUG_ON(!test_bit(I915_RESET_BACKOFF, &error->flags));
> @@ -2016,6 +2018,7 @@ int i915_reset_engine(struct intel_engine_cs *engine, const char *msg)
> struct i915_request *active_request;
> int ret;
>
> + GEM_TRACE("%s flags=%lx\n", engine->name, error->flags);
> GEM_BUG_ON(!test_bit(I915_RESET_ENGINE + engine->id, &error->flags));
>
> active_request = i915_gem_reset_prepare_engine(engine);
> diff --git a/drivers/gpu/drm/i915/selftests/intel_hangcheck.c b/drivers/gpu/drm/i915/selftests/intel_hangcheck.c
> index 9e4e0ad62724..122a32e0a69d 100644
> --- a/drivers/gpu/drm/i915/selftests/intel_hangcheck.c
> +++ b/drivers/gpu/drm/i915/selftests/intel_hangcheck.c
> @@ -979,6 +979,23 @@ static int igt_wait_reset(void *arg)
> return err;
> }
>
> +static int wait_for_others(struct drm_i915_private *i915,
> + struct intel_engine_cs *exclude)
> +{
> + struct intel_engine_cs *engine;
> + enum intel_engine_id id;
> +
> + for_each_engine(engine, i915, id) {
> + if (engine == exclude)
> + continue;
> +
> + if (wait_for(intel_engine_is_idle(engine), 10))
> + return -EIO;
> + }
> +
> + return 0;
> +}
> +
> static int igt_reset_queue(void *arg)
> {
> struct drm_i915_private *i915 = arg;
> @@ -1027,13 +1044,36 @@ static int igt_reset_queue(void *arg)
> i915_request_get(rq);
> __i915_request_add(rq, true);
>
> + /*
> + * XXX We don't handle resetting the kernel context
> + * very well. If we trigger a device reset twice in
> + * quick succession while the kernel context is
> + * executing, we may end up skipping the breadcrumb.
> + * This is really only a problem for the selftest as
> + * normally there is a large interlude between resets
> + * (hangcheck), or we focus on resetting just one
> + * engine and so avoid repeatedly resetting innocents.
> + */
> + err = wait_for_others(i915, engine);
> + if (err) {
> + pr_err("%s(%s): Failed to idle other inactive engines after device reset\n",
> + __func__, engine->name);
> + i915_request_put(rq);
> + i915_request_put(prev);
> +
> + GEM_TRACE_DUMP();
> + i915_gem_set_wedged(i915);
> + goto fini;
> + }
> +
> if (!wait_for_hang(&h, prev)) {
> struct drm_printer p = drm_info_printer(i915->drm.dev);
>
> - pr_err("%s: Failed to start request %x, at %x\n",
> - __func__, prev->fence.seqno, hws_seqno(&h, prev));
> - intel_engine_dump(prev->engine, &p,
> - "%s\n", prev->engine->name);
> + pr_err("%s(%s): Failed to start request %x, at %x\n",
> + __func__, engine->name,
> + prev->fence.seqno, hws_seqno(&h, prev));
> + intel_engine_dump(engine, &p,
> + "%s\n", engine->name);
>
> i915_request_put(rq);
> i915_request_put(prev);
> --
> 2.16.3
>
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