| Message ID | 1437729754-8683-1-git-send-email-michal.winiarski@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Jul 24, 2015 at 11:22:34AM +0200, Micha? Winiarski wrote: > From: Rafa? Sapa?a <rafal.a.sapala@intel.com> > > It is possible to hit a race condition in create_from_prime, when trying > to import a BO that's currently being freed. In case of prime sharing > we'll succesfully get a handle, but fail on get_tiling call, potentially > confusing the caller (and requiring different locking scheme than with > sharing using flink). Wrap fd_to_handle with struct_mutex to force > a more consistent behaviour between prime/flink, convert fprintf to DBG > when handling errors. The race is that the kernel returns us the same file-private handle as the first thread, but that first thread is about to call gem_close (thereby removing the handle from the file completely) and does so between us acquiring the handle and taking the mutex. If we take the mutex, then we acquire the refcnt on the bo prior to the first thread completing its unref (and so preventing the early close). Or we acquire the handle after the earlier close, in which case we are the new owner. Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> -Chris
On Fri, Jul 24, 2015 at 11:51:01AM +0100, Chris Wilson wrote: > On Fri, Jul 24, 2015 at 11:22:34AM +0200, Micha? Winiarski wrote: > > From: Rafa? Sapa?a <rafal.a.sapala@intel.com> > > > > It is possible to hit a race condition in create_from_prime, when trying > > to import a BO that's currently being freed. In case of prime sharing > > we'll succesfully get a handle, but fail on get_tiling call, potentially > > confusing the caller (and requiring different locking scheme than with > > sharing using flink). Wrap fd_to_handle with struct_mutex to force > > a more consistent behaviour between prime/flink, convert fprintf to DBG > > when handling errors. > > The race is that the kernel returns us the same file-private handle as > the first thread, but that first thread is about to call gem_close > (thereby removing the handle from the file completely) and does so > between us acquiring the handle and taking the mutex. If we take > the mutex, then we acquire the refcnt on the bo prior to the first > thread completing its unref (and so preventing the early close). Or we > acquire the handle after the earlier close, in which case we are the new > owner. > > Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Thanks for the patch & review, pushed.
diff --git a/intel/intel_bufmgr_gem.c b/intel/intel_bufmgr_gem.c index b1c3b3a..ed4ffd2 100644 --- a/intel/intel_bufmgr_gem.c +++ b/intel/intel_bufmgr_gem.c @@ -2728,14 +2728,19 @@ drm_intel_bo_gem_create_from_prime(drm_intel_bufmgr *bufmgr, int prime_fd, int s struct drm_i915_gem_get_tiling get_tiling; drmMMListHead *list; + pthread_mutex_lock(&bufmgr_gem->lock); ret = drmPrimeFDToHandle(bufmgr_gem->fd, prime_fd, &handle); + if (ret) { + DBG("create_from_prime: failed to obtain handle from fd: %s\n", strerror(errno)); + pthread_mutex_unlock(&bufmgr_gem->lock); + return NULL; + } /* * 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 */ - pthread_mutex_lock(&bufmgr_gem->lock); for (list = bufmgr_gem->named.next; list != &bufmgr_gem->named; list = list->next) { @@ -2747,12 +2752,6 @@ drm_intel_bo_gem_create_from_prime(drm_intel_bufmgr *bufmgr, int prime_fd, int s } } - if (ret) { - fprintf(stderr,"ret is %d %d\n", ret, errno); - pthread_mutex_unlock(&bufmgr_gem->lock); - return NULL; - } - bo_gem = calloc(1, sizeof(*bo_gem)); if (!bo_gem) { pthread_mutex_unlock(&bufmgr_gem->lock); @@ -2793,6 +2792,7 @@ drm_intel_bo_gem_create_from_prime(drm_intel_bufmgr *bufmgr, int prime_fd, int s DRM_IOCTL_I915_GEM_GET_TILING, &get_tiling); if (ret != 0) { + DBG("create_from_prime: failed to get tiling: %s\n", strerror(errno)); drm_intel_gem_bo_unreference(&bo_gem->bo); return NULL; }