On Fri, Sep 12, 2014 at 11:27:07AM +0100, Lionel Landwerlin wrote:
When using Mesa and LibVA in the same process, one would like to be able bind buffers from the output of the decoder to a GL texture through an EGLImage.
LibVA can reuse buffers allocated by Gbm through a file descriptor. It will then wrap it into a drm_intel_bo with drm_intel_bo_gem_create_from_prime().
The problem at the moment is that both library get a different drm_intel_bufmgr object when they call drm_intel_bufmgr_gem_init() even though they're using the same drm file descriptor. As a result, instead of manipulating the same buffer object for a given file descriptor, they get 2 different drm_intel_bo objects and 2 different refcounts, leading one of the library to get errors from the kernel on invalid BO when one of the 2 library is done with a shared buffer.
This patch modifies drm_intel_bufmgr_gem_init() so, given a file descriptor, it will look for an already existing drm_intel_bufmgr using the same file descriptor and return that object.
Signed-off-by: Lionel Landwerlin lionel.g.landwerlin@intel.com
So close.
+static void +drm_intel_bufmgr_gem_unref(drm_intel_bufmgr *bufmgr) +{
- drm_intel_bufmgr_gem *bufmgr_gem = (drm_intel_bufmgr_gem *)bufmgr;
- if (atomic_dec_and_test(&bufmgr_gem->refcount)) {
assert(pthread_mutex_lock(&bufmgr_list_mutex) == 0);
(Oh, don't use assert for expressions with side-effects)
if (atomic_read(&bufmgr_gem->refcount)) {
As a thought exercise, now consider what happens if thread B grabs a reference to this bufmgr and frees it all before this thread wakes up?
Double free, kaboom.
This does have to be an atomic_add_unless, which does not yet exist in libdrm:
static inline int atomic_add_unless(atomic_t *v, int add, int unless) { int c, old; c = atomic_read(v); while (c != unless && (old = atomic_cmpxchg(v, c, c + add)) != c) c = old; return c == unless; }
static void drm_intel_bufmgr_gem_unref(drm_intel_bufmgr *bufmgr) { drm_intel_bufmgr_gem *bufmgr_gem = (drm_intel_bufmgr_gem *)bufmgr;
if (atomic_add_unless(&bufmgr_gem->refcount, -1, 1)) { pthread_mutex_lock(&bufmgr_list_mutex); if (atomic_dec_and_test(&bufmgr_gem->refcount)) { free stuff; } pthread_mutex_unlock(&bufmgr_list_mutex); } } -Chris