linux-kernel - [PATCH] drm/i915: annote drop_caches debugfs interface with lockdep

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Date:   Sun, 12 Mar 2017 21:53:40 +0100
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     Intel Graphics Development <intel-gfx@...ts.freedesktop.org>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: [PATCH] drm/i915: annote drop_caches debugfs interface with lockdep

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.

v2: Need to EXPORT_SYMBOL_GPL to make it compile as a module.

v3: Fixup rebase fail (spotted by Chris).

Cc: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>

--

Peter/Ingo,

We want this to validate the i915 shrinker locking in our fast tests
without thrashing badly (that takes too long, we can only thrash in
the extended runs). Can you pls take a look and if it's ok ack for
merging through drm-intel.git?

Thanks, Daniel
---
 drivers/gpu/drm/i915/i915_debugfs.c | 2 ++
 kernel/locking/lockdep.c            | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 82fb005a5e22..fbe761a3f5bd 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -4273,6 +4273,7 @@ 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);
 
@@ -4281,6 +4282,7 @@ i915_drop_caches_set(void *data, u64 val)
 
 	if (val & DROP_SHRINK_ALL)
 		i915_gem_shrink_all(dev_priv);
+	lockdep_clear_current_reclaim_state();
 
 unlock:
 	mutex_unlock(&dev->struct_mutex);
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 12e38c213b70..508cbf31d43e 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3856,11 +3856,13 @@ void lockdep_set_current_reclaim_state(gfp_t gfp_mask)
 {
 	current->lockdep_reclaim_gfp = gfp_mask;
 }
+EXPORT_SYMBOL_GPL(lockdep_set_current_reclaim_state);
 
 void lockdep_clear_current_reclaim_state(void)
 {
 	current->lockdep_reclaim_gfp = 0;
 }
+EXPORT_SYMBOL_GPL(lockdep_clear_current_reclaim_state);
 
 #ifdef CONFIG_LOCK_STAT
 static int
-- 
2.11.0