From a35f2e2b83a789e189a501ebd722bc9a1310eb05 Mon Sep 17 00:00:00 2001 From: Roland Dreier Date: Fri, 6 Feb 2009 17:48:09 -0800 Subject: drm/i915: Fix potential AB-BA deadlock in i915_gem_execbuffer() Lockdep warns that i915_gem_execbuffer() can trigger a page fault (which takes mmap_sem) while holding dev->struct_mutex, while drm_vm_open() (which is called with mmap_sem already held) takes dev->struct_mutex. So this is a potential AB-BA deadlock. The way that i915_gem_execbuffer() triggers a page fault is by doing copy_to_user() when returning new buffer offsets back to userspace; however there is no reason to hold the struct_mutex when doing this copy, since what is being copied is the contents of an array private to i915_gem_execbuffer() anyway. So we can fix the potential deadlock (and get rid of the lockdep warning) by simply moving the copy_to_user() outside of where struct_mutex is held. This fixes . Reported-by: Jesse Brandeburg Tested-by: Jesse Brandeburg Signed-off-by: Roland Dreier Signed-off-by: Eric Anholt Signed-off-by: Dave Airlie --- drivers/gpu/drm/i915/i915_gem.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) (limited to 'drivers/gpu') diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 55f4c060fa0..ff0d94dd355 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2634,15 +2634,6 @@ i915_gem_execbuffer(struct drm_device *dev, void *data, i915_verify_inactive(dev, __FILE__, __LINE__); - /* Copy the new buffer offsets back to the user's exec list. */ - ret = copy_to_user((struct drm_i915_relocation_entry __user *) - (uintptr_t) args->buffers_ptr, - exec_list, - sizeof(*exec_list) * args->buffer_count); - if (ret) - DRM_ERROR("failed to copy %d exec entries " - "back to user (%d)\n", - args->buffer_count, ret); err: for (i = 0; i < pinned; i++) i915_gem_object_unpin(object_list[i]); @@ -2652,6 +2643,18 @@ err: mutex_unlock(&dev->struct_mutex); + if (!ret) { + /* Copy the new buffer offsets back to the user's exec list. */ + ret = copy_to_user((struct drm_i915_relocation_entry __user *) + (uintptr_t) args->buffers_ptr, + exec_list, + sizeof(*exec_list) * args->buffer_count); + if (ret) + DRM_ERROR("failed to copy %d exec entries " + "back to user (%d)\n", + args->buffer_count, ret); + } + pre_mutex_err: drm_free(object_list, sizeof(*object_list) * args->buffer_count, DRM_MEM_DRIVER); -- cgit v1.2.3-70-g09d2