[Intel-gfx] [PATCH] RFC: drm/i915: annote drop_caches debugfs interface with lockdep

[Daniel Vetter]

The trouble we have is that we can't really test all the shrinker
recursion stuff exhaustively in BAT because any kind of thrashing
stress test just takes too long.

But that leaves a really big gap open, since shrinker recursions are
one of the most annoying bugs. Now lockdep already has support for
checking allocation deadlocks:

- Direct reclaim paths are marked up with
  lockdep_set_current_reclaim_state() and
  lockdep_clear_current_reclaim_state().

- Any allocation paths are marked with lockdep_trace_alloc().

If we simply mark up our debugfs with the reclaim annotations, any
code and locks taken in there will automatically complete the picture
with any allocation paths we already have, as long as we have a simple
testcase in BAT which throws out a few objects using this interface.
Not stress test or thrashing needed at all.

Just a quick hack as an RFC after a short discussion with Chris on
irc.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index fd0aa29e0c3b..72a73bb08a1e 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -4268,11 +4268,13 @@ i915_drop_caches_set(void *data, u64 val)
 	if (val & (DROP_RETIRE | DROP_ACTIVE))
 		i915_gem_retire_requests(dev_priv);
 
+	lockdep_set_current_reclaim_state(GFP_KERNEL);
 	if (val & DROP_BOUND)
 		i915_gem_shrink(dev_priv, LONG_MAX, I915_SHRINK_BOUND);
 
 	if (val & DROP_UNBOUND)
 		i915_gem_shrink(dev_priv, LONG_MAX, I915_SHRINK_UNBOUND);
+	lockdep_clear_current_reclaim_state();
 
 unlock:
 	mutex_unlock(&dev->struct_mutex);
-- 
2.11.0