[PATCH 5.10 024/142] drm/i915: Always flush the active worker before returning from the wait

Greg Kroah-Hartman
2021-02-02T20:06:50Z

From: Chris Wilson <chris@chris-wilson.co.uk>

commit f6e98a1809faa02f40e0d089d6cfc1aa372a34c0 upstream.

The first thing the active retirement worker does is decrement the
i915_active count.

The first thing we do during i915_active_wait is try to increment the
i915_active count, but only if already active [non-zero].

The wait may see that the retirement is already started and so marked the
i915_active as idle, and skip waiting for the retirement handler.
However, the caller of i915_active_wait may immediately free the
i915_active upon returning (e.g. i915_vma_destroy) so we must not return
before the concurrent access from the worker is completed. We must
always flush the worker.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2473
Fixes: 274cbf20fd10 ("drm/i915: Push the i915_active.retire into a worker")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v5.5+
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210121232807.16618-1-chris@chris-wilson.co.uk
(cherry picked from commit 977a372e972cb42799746c284035a33c64ebace9)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index 10a865f3dc09..9ed19b8bca60 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -631,24 +631,26 @@ static int flush_lazy_signals(struct i915_active *ref)

int __i915_active_wait(struct i915_active *ref, int state)
{
- int err;
-
might_sleep();

- if (!i915_active_acquire_if_busy(ref))
- return 0;
-
/* Any fence added after the wait begins will not be auto-signaled */
- err = flush_lazy_signals(ref);
- i915_active_release(ref);
- if (err)
- return err;
+ if (i915_active_acquire_if_busy(ref)) {
+ int err;

- if (!i915_active_is_idle(ref) &&
- ___wait_var_event(ref, i915_active_is_idle(ref),
- state, 0, 0, schedule()))
- return -EINTR;
+ err = flush_lazy_signals(ref);
+ i915_active_release(ref);
+ if (err)
+ return err;

+ if (___wait_var_event(ref, i915_active_is_idle(ref),
+ state, 0, 0, schedule()))
+ return -EINTR;
+ }
+
+ /*
+ * After the wait is complete, the caller may free the active.
+ * We have to flush any concurrent retirement before returning.
+ */
flush_work(&ref->work);
return 0;
}