Messages in this thread Patch in this message | | | From | Eric Anholt <> | Subject | [PATCH] drm: Fix lock order reversal between mmap_sem and struct_mutex. | Date | Tue, 17 Feb 2009 16:59:46 -0800 |
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The basic problem was mmap_sem (do_mmap()) -> struct_mutex (drm_gem_mmap(), i915_gem_fault()) struct_mutex (i915_gem_execbuffer()) -> mmap_sem (copy_from/to_user())
We have plenty of places where we want to hold device state the same (struct_mutex) while we move a non-trivial amount of data (copy_from/to_user()), such as i915_gem_pwrite(). Solve this by moving the easy things that needed struct_mutex with mmap_sem held to using a lock to cover just those data structures (offset hash and offset manager), and do trylock and reschedule in fault.
Signed-off-by: Eric Anholt <eric@anholt.net> --- drivers/gpu/drm/drm_gem.c | 8 ++++---- drivers/gpu/drm/i915/i915_gem.c | 15 ++++++++++++++- include/drm/drmP.h | 1 + 3 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index 88d3368..13a0184 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -97,6 +97,7 @@ drm_gem_init(struct drm_device *dev) dev->mm_private = mm; + mutex_init(&mm->offset_mutex); if (drm_ht_create(&mm->offset_hash, 19)) { drm_free(mm, sizeof(struct drm_gem_mm), DRM_MEM_MM); return -ENOMEM; @@ -508,10 +509,9 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma) unsigned long prot; int ret = 0; - mutex_lock(&dev->struct_mutex); - + mutex_lock(&mm->offset_mutex); if (drm_ht_find_item(&mm->offset_hash, vma->vm_pgoff, &hash)) { - mutex_unlock(&dev->struct_mutex); + mutex_unlock(&mm->offset_mutex); return drm_mmap(filp, vma); } @@ -556,7 +556,7 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma) drm_vm_open_locked(vma); out_unlock: - mutex_unlock(&dev->struct_mutex); + mutex_unlock(&mm->offset_mutex); return ret; } diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index ac534c9..da9a2cb 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -573,8 +573,16 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf) page_offset = ((unsigned long)vmf->virtual_address - vma->vm_start) >> PAGE_SHIFT; + /* Get the struct mutex before accessing GEM data structures, but + * keep the struct_mutex -> mmap_sem lock ordering so that we don't + * need to mangle pwrite/pread to allow mmap_sem -> struct_mutex. + */ + if (!mutex_trylock(&dev->struct_mutex)) { + need_resched(); + return VM_FAULT_NOPAGE; + } + /* Now bind it into the GTT if needed */ - mutex_lock(&dev->struct_mutex); if (!obj_priv->gtt_space) { ret = i915_gem_object_bind_to_gtt(obj, obj_priv->gtt_alignment); if (ret) { @@ -646,6 +654,7 @@ i915_gem_create_mmap_offset(struct drm_gem_object *obj) map->size = obj->size; map->handle = obj; + mutex_lock(&mm->offset_mutex); /* Get a DRM GEM mmap offset allocated... */ list->file_offset_node = drm_mm_search_free(&mm->offset_manager, obj->size / PAGE_SIZE, 0, 0); @@ -671,12 +680,14 @@ i915_gem_create_mmap_offset(struct drm_gem_object *obj) /* By now we should be all set, any drm_mmap request on the offset * below will get to our mmap & fault handler */ obj_priv->mmap_offset = ((uint64_t) list->hash.key) << PAGE_SHIFT; + mutex_unlock(&mm->offset_mutex); return 0; out_free_mm: drm_mm_put_block(list->file_offset_node); out_free_list: + mutex_unlock(&mm->offset_mutex); drm_free(list->map, sizeof(struct drm_map_list), DRM_MEM_DRIVER); return ret; @@ -690,6 +701,7 @@ i915_gem_free_mmap_offset(struct drm_gem_object *obj) struct drm_gem_mm *mm = dev->mm_private; struct drm_map_list *list; + mutex_lock(&mm->offset_mutex); list = &obj->map_list; drm_ht_remove_item(&mm->offset_hash, &list->hash); @@ -704,6 +716,7 @@ i915_gem_free_mmap_offset(struct drm_gem_object *obj) } obj_priv->mmap_offset = 0; + mutex_unlock(&mm->offset_mutex); } /** diff --git a/include/drm/drmP.h b/include/drm/drmP.h index e5f4ae9..04f765b 100644 --- a/include/drm/drmP.h +++ b/include/drm/drmP.h @@ -570,6 +570,7 @@ struct drm_ati_pcigart_info { struct drm_gem_mm { struct drm_mm offset_manager; /**< Offset mgmt for buffer objects */ struct drm_open_hash offset_hash; /**< User token hash table for maps */ + struct mutex offset_mutex; /**< covers offset_manager and offset_hash */ }; /** -- 1.5.6.5
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