[Mesa-dev] [PATCH] intel: Track known prime buffers for re-use

[Keith Packard]

If the application sends us a file descriptor pointing at a prime
buffer that we've already got, we have to re-use the same bo_gem
structure or chaos will result.

Track the set of all known prime objects and look to see if the kernel
has returned one of those for a new file descriptor.

Signed-off-by: Keith Packard <keithp at keithp.com>
---

This one took a while to find -- multiple bo_gem structs pointing at
the same gem handle would either cause the object to be destroyed
before we were done using it, or we'd end up sending the same
gem_handle for multiple buffers.

This looks a lot like the named object handling stuff, as one would
expect.

 intel/intel_bufmgr_gem.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/intel/intel_bufmgr_gem.c b/intel/intel_bufmgr_gem.c
index df6fcec..2897bb2 100644
--- a/intel/intel_bufmgr_gem.c
+++ b/intel/intel_bufmgr_gem.c
@@ -112,6 +112,7 @@ typedef struct _drm_intel_bufmgr_gem {
 
 	drmMMListHead named;
 	drmMMListHead vma_cache;
+        drmMMListHead prime;
 	int vma_count, vma_open, vma_max;
 
 	uint64_t gtt_size;
@@ -2451,8 +2452,25 @@ drm_intel_bo_gem_create_from_prime(drm_intel_bufmgr *bufmgr, int prime_fd, int s
 	uint32_t handle;
 	drm_intel_bo_gem *bo_gem;
 	struct drm_i915_gem_get_tiling get_tiling;
+	drmMMListHead *list;
 
 	ret = drmPrimeFDToHandle(bufmgr_gem->fd, prime_fd, &handle);
+
+	/*
+	 * See if the kernel has already returned this buffer to us. Just as
+	 * for named buffers, we must not create two bo's pointing at the same
+	 * kernel object
+	 */
+	for (list = bufmgr_gem->prime.next;
+	     list != &bufmgr_gem->prime;
+	     list = list->next) {
+		bo_gem = DRMLISTENTRY(drm_intel_bo_gem, list, name_list);
+		if (bo_gem->gem_handle == handle) {
+			drm_intel_gem_bo_reference(&bo_gem->bo);
+			return &bo_gem->bo;
+		}
+	}
+
 	if (ret) {
 	  fprintf(stderr,"ret is %d %d\n", ret, errno);
 		return NULL;
@@ -2487,8 +2505,8 @@ drm_intel_bo_gem_create_from_prime(drm_intel_bufmgr *bufmgr, int prime_fd, int s
 	bo_gem->has_error = false;
 	bo_gem->reusable = false;
 
-	DRMINITLISTHEAD(&bo_gem->name_list);
 	DRMINITLISTHEAD(&bo_gem->vma_list);
+	DRMLISTADDTAIL(&bo_gem->name_list, &bufmgr_gem->prime);
 
 	VG_CLEAR(get_tiling);
 	get_tiling.handle = bo_gem->gem_handle;
@@ -3301,5 +3319,7 @@ drm_intel_bufmgr_gem_init(int fd, int batch_size)
 	DRMINITLISTHEAD(&bufmgr_gem->vma_cache);
 	bufmgr_gem->vma_max = -1; /* unlimited by default */
 
+	DRMINITLISTHEAD(&bufmgr_gem->prime);
+
 	return &bufmgr_gem->bufmgr;
 }
-- 
1.8.4.3