drm/i915: Mark the end of intel_ring_begin() and check in intel_ring_advance()

It is required that the caller declare the exact number of dwords they
wish to write into the ring. This is required for two reasons, we need
to allocate sufficient space for the entire command packet and we need
to be sure that the contents are completely written to avoid executing
stale data. The current interface requires for any bug to be caught in
review, the reader has to carefully count the number of
intel_ring_emit() between intel_ring_begin() and intel_ring_advance().
If we record the end of the packet of each intel_ring_begin() we can
also have CI check for us.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170206170502.30944-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
index a585d47c420af15fea90fc6f5d862d24e4d07087..412fa2794cbb40be7e5d0de6c74fce0b26bec874 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.h
+++ b/drivers/gpu/drm/i915/i915_gem.h
@@ -28,9 +28,18 @@
 #ifdef CONFIG_DRM_I915_DEBUG_GEM
 #define GEM_BUG_ON(expr) BUG_ON(expr)
 #define GEM_WARN_ON(expr) WARN_ON(expr)
+
+#define GEM_BUG_ONLY(expr) expr
+#define GEM_BUG_ONLY_DECLARE(var) var
+#define GEM_BUG_ONLY_ON(expr) GEM_BUG_ON(expr)
+
 #else
 #define GEM_BUG_ON(expr) BUILD_BUG_ON_INVALID(expr)
 #define GEM_WARN_ON(expr) (BUILD_BUG_ON_INVALID(expr), 0)
+
+#define GEM_BUG_ONLY(expr) do { } while (0)
+#define GEM_BUG_ONLY_DECLARE(var)
+#define GEM_BUG_ONLY_ON(expr)
 #endif
 
 #define I915_NUM_ENGINES 5

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index d32cbba25d98c973d45ef8b12a46524a667f1257..383083ef221010e6985422705b626472523ca20a 100644 (file)
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2238,6 +2238,7 @@ int intel_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
 
        ring->space -= bytes;
        GEM_BUG_ON(ring->space < 0);
+       GEM_BUG_ONLY(ring->advance = ring->tail + bytes);
        return 0;
 }
 

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index b9c15cd40fbfe246b62fc0896dd94d6ce8e74e8e..2c6d3655985e360e2b322cf27d811bbf3978757b 100644 (file)
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -144,6 +144,8 @@ struct intel_ring {
 
        u32 head;
        u32 tail;
+       GEM_BUG_ONLY_DECLARE(u32 advance);
+
        int space;
        int size;
        int effective_size;
@@ -516,6 +518,7 @@ static inline void intel_ring_advance(struct intel_ring *ring)
         * reserved for the command packet (i.e. the value passed to
         * intel_ring_begin()).
         */
+       GEM_BUG_ONLY_ON(ring->tail != ring->advance);
 }
 
 static inline u32 intel_ring_offset(struct intel_ring *ring, void *addr)