This patch moves the non-dynamic dma-buf users over to the dynamic locking specification. The strict locking convention prevents deadlock situation for dma-buf importers and exporters.
Previously the "unlocked" versions of the dma-buf API functions weren't taking the reservation lock and this patch makes them to take the lock.
Intel and AMD GPU drivers already were mapping imported dma-bufs under the held lock, hence the "locked" variant of the functions are added for them and the drivers are updated to use the "locked" versions.
Signed-off-by: Dmitry Osipenko dmitry.osipenko@collabora.com --- Documentation/driver-api/dma-buf.rst | 6 + drivers/dma-buf/dma-buf.c | 186 ++++++++++++++++----- drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 4 +- drivers/gpu/drm/drm_prime.c | 4 +- drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 8 +- include/linux/dma-buf.h | 28 ++-- 6 files changed, 179 insertions(+), 57 deletions(-)
diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst index 36a76cbe9095..622b8156d212 100644 --- a/Documentation/driver-api/dma-buf.rst +++ b/Documentation/driver-api/dma-buf.rst @@ -119,6 +119,12 @@ DMA Buffer ioctls
.. kernel-doc:: include/uapi/linux/dma-buf.h
+DMA-BUF locking convention +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: drivers/dma-buf/dma-buf.c + :doc: locking convention + Kernel Functions and Structures Reference ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index d16237a6ffaa..bfdd551c7571 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -559,7 +559,7 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags) * 2. Userspace passes this file-descriptors to all drivers it wants this buffer * to share with: First the file descriptor is converted to a &dma_buf using * dma_buf_get(). Then the buffer is attached to the device using - * dma_buf_attach(). + * dma_buf_attach_unlocked(). * * Up to this stage the exporter is still free to migrate or reallocate the * backing storage. @@ -569,8 +569,8 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags) * dma_buf_map_attachment() and dma_buf_unmap_attachment(). * * 4. Once a driver is done with a shared buffer it needs to call - * dma_buf_detach() (after cleaning up any mappings) and then release the - * reference acquired with dma_buf_get() by calling dma_buf_put(). + * dma_buf_detach_unlocked() (after cleaning up any mappings) and then + * release the reference acquired with dma_buf_get() by calling dma_buf_put(). * * For the detailed semantics exporters are expected to implement see * &dma_buf_ops. @@ -794,6 +794,63 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach, return sg_table; }
+/** + * DOC: locking convention + * + * In order to avoid deadlock situations between dma-buf exports and importers, + * all dma-buf API users must follow the common dma-buf locking convention. + * + * Convention for importers + * + * 1. Importers must hold the dma-buf reservation lock when calling these + * functions: + * + * - dma_buf_pin() + * - dma_buf_unpin() + * - dma_buf_move_notify() + * - dma_buf_map_attachment_locked() + * - dma_buf_unmap_attachment_locked() + * + * 2. Importers must not hold the dma-buf reservation lock when calling these + * functions: + * + * - dma_buf_attach_unlocked() + * - dma_buf_dynamic_attach_unlocked() + * - dma_buf_detach_unlocked() + * - dma_buf_export( + * - dma_buf_fd() + * - dma_buf_get() + * - dma_buf_put() + * - dma_buf_begin_cpu_access() + * - dma_buf_end_cpu_access() + * - dma_buf_map_attachment_unlocked() + * - dma_buf_unmap_attachment_unlocked() + * - dma_buf_vmap_unlocked() + * - dma_buf_vunmap_unlocked() + * + * Convention for exporters + * + * 1. These &dma_buf_ops callbacks are invoked with unlocked dma-buf + * reservation and exporter can take the lock: + * + * - &dma_buf_ops.attach() + * - &dma_buf_ops.detach() + * - &dma_buf_ops.release() + * - &dma_buf_ops.begin_cpu_access() + * - &dma_buf_ops.end_cpu_access() + * + * 2. These &dma_buf_ops callbacks are invoked with locked dma-buf + * reservation and exporter can't take the lock: + * + * - &dma_buf_ops.pin() + * - &dma_buf_ops.unpin() + * - &dma_buf_ops.map_dma_buf() + * - &dma_buf_ops.unmap_dma_buf() + * - &dma_buf_ops.mmap() + * - &dma_buf_ops.vmap() + * - &dma_buf_ops.vunmap() + */ + /** * dma_buf_dynamic_attach_unlocked - Add the device to dma_buf's attachments list * @dmabuf: [in] buffer to attach device to. @@ -802,7 +859,7 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach, * @importer_priv: [in] importer private pointer for the attachment * * Returns struct dma_buf_attachment pointer for this attachment. Attachments - * must be cleaned up by calling dma_buf_detach(). + * must be cleaned up by calling dma_buf_detach_unlocked(). * * Optionally this calls &dma_buf_ops.attach to allow device-specific attach * functionality. @@ -858,8 +915,8 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev, dma_buf_is_dynamic(dmabuf)) { struct sg_table *sgt;
+ dma_resv_lock(attach->dmabuf->resv, NULL); if (dma_buf_is_dynamic(attach->dmabuf)) { - dma_resv_lock(attach->dmabuf->resv, NULL); ret = dmabuf->ops->pin(attach); if (ret) goto err_unlock; @@ -872,8 +929,7 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev, ret = PTR_ERR(sgt); goto err_unpin; } - if (dma_buf_is_dynamic(attach->dmabuf)) - dma_resv_unlock(attach->dmabuf->resv); + dma_resv_unlock(attach->dmabuf->resv); attach->sgt = sgt; attach->dir = DMA_BIDIRECTIONAL; } @@ -889,8 +945,7 @@ dma_buf_dynamic_attach_unlocked(struct dma_buf *dmabuf, struct device *dev, dmabuf->ops->unpin(attach);
err_unlock: - if (dma_buf_is_dynamic(attach->dmabuf)) - dma_resv_unlock(attach->dmabuf->resv); + dma_resv_unlock(attach->dmabuf->resv);
dma_buf_detach_unlocked(dmabuf, attach); return ERR_PTR(ret); @@ -927,7 +982,7 @@ static void __unmap_dma_buf(struct dma_buf_attachment *attach, * @dmabuf: [in] buffer to detach from. * @attach: [in] attachment to be detached; is free'd after this call. * - * Clean up a device attachment obtained by calling dma_buf_attach(). + * Clean up a device attachment obtained by calling dma_buf_attach_unlocked(). * * Optionally this calls &dma_buf_ops.detach for device-specific detach. */ @@ -937,21 +992,19 @@ void dma_buf_detach_unlocked(struct dma_buf *dmabuf, if (WARN_ON(!dmabuf || !attach)) return;
+ dma_resv_lock(attach->dmabuf->resv, NULL); + if (attach->sgt) { - if (dma_buf_is_dynamic(attach->dmabuf)) - dma_resv_lock(attach->dmabuf->resv, NULL);
__unmap_dma_buf(attach, attach->sgt, attach->dir);
- if (dma_buf_is_dynamic(attach->dmabuf)) { + if (dma_buf_is_dynamic(attach->dmabuf)) dmabuf->ops->unpin(attach); - dma_resv_unlock(attach->dmabuf->resv); - } } - - dma_resv_lock(dmabuf->resv, NULL); list_del(&attach->node); + dma_resv_unlock(dmabuf->resv); + if (dmabuf->ops->detach) dmabuf->ops->detach(dmabuf, attach);
@@ -1030,10 +1083,11 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, DMA_BUF); * * Important: Dynamic importers must wait for the exclusive fence of the struct * dma_resv attached to the DMA-BUF first. + * + * Importer is responsible for holding dmabuf's reservation lock. */ -struct sg_table * -dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach, - enum dma_data_direction direction) +struct sg_table *dma_buf_map_attachment_locked(struct dma_buf_attachment *attach, + enum dma_data_direction direction) { struct sg_table *sg_table; int r; @@ -1043,8 +1097,7 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach, if (WARN_ON(!attach || !attach->dmabuf)) return ERR_PTR(-EINVAL);
- if (dma_buf_attachment_is_dynamic(attach)) - dma_resv_assert_held(attach->dmabuf->resv); + dma_resv_assert_held(attach->dmabuf->resv);
if (attach->sgt) { /* @@ -1059,7 +1112,6 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach, }
if (dma_buf_is_dynamic(attach->dmabuf)) { - dma_resv_assert_held(attach->dmabuf->resv); if (!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) { r = attach->dmabuf->ops->pin(attach); if (r) @@ -1099,10 +1151,38 @@ dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach, #endif /* CONFIG_DMA_API_DEBUG */ return sg_table; } +EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_locked, DMA_BUF); + +/** + * dma_buf_map_attachment_unlocked - Returns the scatterlist table of the attachment; + * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the + * dma_buf_ops. + * @attach: [in] attachment whose scatterlist is to be returned + * @direction: [in] direction of DMA transfer + * + * Unlocked variant of dma_buf_map_attachment_locked(). + */ +struct sg_table * +dma_buf_map_attachment_unlocked(struct dma_buf_attachment *attach, + enum dma_data_direction direction) +{ + struct sg_table *sg_table; + + might_sleep(); + + if (WARN_ON(!attach || !attach->dmabuf)) + return ERR_PTR(-EINVAL); + + dma_resv_lock(attach->dmabuf->resv, NULL); + sg_table = dma_buf_map_attachment_locked(attach, direction); + dma_resv_unlock(attach->dmabuf->resv); + + return sg_table; +} EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_unlocked, DMA_BUF);
/** - * dma_buf_unmap_attachment_unlocked - unmaps and decreases usecount of the buffer;might + * dma_buf_unmap_attachment_locked - unmaps and decreases usecount of the buffer;might * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of * dma_buf_ops. * @attach: [in] attachment to unmap buffer from @@ -1110,31 +1190,51 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_map_attachment_unlocked, DMA_BUF); * @direction: [in] direction of DMA transfer * * This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment(). + * + * Importer is responsible for holding dmabuf's reservation lock. */ -void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach, - struct sg_table *sg_table, - enum dma_data_direction direction) +void dma_buf_unmap_attachment_locked(struct dma_buf_attachment *attach, + struct sg_table *sg_table, + enum dma_data_direction direction) { might_sleep();
- if (WARN_ON(!attach || !attach->dmabuf || !sg_table)) - return; - - if (dma_buf_attachment_is_dynamic(attach)) - dma_resv_assert_held(attach->dmabuf->resv); + dma_resv_assert_held(attach->dmabuf->resv);
if (attach->sgt == sg_table) return;
- if (dma_buf_is_dynamic(attach->dmabuf)) - dma_resv_assert_held(attach->dmabuf->resv); - __unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) && !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY)) dma_buf_unpin(attach); } +EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment_locked, DMA_BUF); + +/** + * dma_buf_unmap_attachment_unlocked - unmaps and decreases usecount of the buffer;might + * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of + * dma_buf_ops. + * @attach: [in] attachment to unmap buffer from + * @sg_table: [in] scatterlist info of the buffer to unmap + * @direction: [in] direction of DMA transfer + * + * Unlocked variant of dma_buf_unmap_attachment_locked(). + */ +void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach, + struct sg_table *sg_table, + enum dma_data_direction direction) +{ + might_sleep(); + + if (WARN_ON(!attach || !attach->dmabuf || !sg_table)) + return; + + dma_resv_lock(attach->dmabuf->resv, NULL); + dma_buf_unmap_attachment_locked(attach, sg_table, direction); + dma_resv_unlock(attach->dmabuf->resv); +} EXPORT_SYMBOL_NS_GPL(dma_buf_unmap_attachment_unlocked, DMA_BUF);
/** @@ -1174,8 +1274,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_move_notify, DMA_BUF); * * Interfaces:: * - * void *dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map) - * void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map) + * void *dma_buf_vmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map) + * void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map) * * The vmap call can fail if there is no vmap support in the exporter, or if * it runs out of vmalloc space. Note that the dma-buf layer keeps a reference @@ -1348,6 +1448,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_end_cpu_access, DMA_BUF); int dma_buf_mmap_unlocked(struct dma_buf *dmabuf, struct vm_area_struct *vma, unsigned long pgoff) { + int ret; + if (WARN_ON(!dmabuf || !vma)) return -EINVAL;
@@ -1368,7 +1470,11 @@ int dma_buf_mmap_unlocked(struct dma_buf *dmabuf, struct vm_area_struct *vma, vma_set_file(vma, dmabuf->file); vma->vm_pgoff = pgoff;
- return dmabuf->ops->mmap(dmabuf, vma); + dma_resv_lock(dmabuf->resv, NULL); + ret = dmabuf->ops->mmap(dmabuf, vma); + dma_resv_unlock(dmabuf->resv); + + return ret; } EXPORT_SYMBOL_NS_GPL(dma_buf_mmap_unlocked, DMA_BUF);
@@ -1401,6 +1507,7 @@ int dma_buf_vmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map) if (!dmabuf->ops->vmap) return -EINVAL;
+ dma_resv_lock(dmabuf->resv, NULL); mutex_lock(&dmabuf->lock); if (dmabuf->vmapping_counter) { dmabuf->vmapping_counter++; @@ -1422,6 +1529,7 @@ int dma_buf_vmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)
out_unlock: mutex_unlock(&dmabuf->lock); + dma_resv_unlock(dmabuf->resv); return ret; } EXPORT_SYMBOL_NS_GPL(dma_buf_vmap_unlocked, DMA_BUF); @@ -1440,6 +1548,7 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map) BUG_ON(dmabuf->vmapping_counter == 0); BUG_ON(!iosys_map_is_equal(&dmabuf->vmap_ptr, map));
+ dma_resv_lock(dmabuf->resv, NULL); mutex_lock(&dmabuf->lock); if (--dmabuf->vmapping_counter == 0) { if (dmabuf->ops->vunmap) @@ -1447,6 +1556,7 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map) iosys_map_clear(&dmabuf->vmap_ptr); } mutex_unlock(&dmabuf->lock); + dma_resv_unlock(dmabuf->resv); } EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap_unlocked, DMA_BUF);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c index dd6ac1606316..1b426116c22e 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c @@ -882,7 +882,7 @@ static int amdgpu_ttm_backend_bind(struct ttm_device *bdev, struct sg_table *sgt;
attach = gtt->gobj->import_attach; - sgt = dma_buf_map_attachment_unlocked(attach, DMA_BIDIRECTIONAL); + sgt = dma_buf_map_attachment_locked(attach, DMA_BIDIRECTIONAL); if (IS_ERR(sgt)) return PTR_ERR(sgt);
@@ -1007,7 +1007,7 @@ static void amdgpu_ttm_backend_unbind(struct ttm_device *bdev, struct dma_buf_attachment *attach;
attach = gtt->gobj->import_attach; - dma_buf_unmap_attachment_unlocked(attach, ttm->sg, DMA_BIDIRECTIONAL); + dma_buf_unmap_attachment_locked(attach, ttm->sg, DMA_BIDIRECTIONAL); ttm->sg = NULL; }
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 1bd234fd21a5..b75ef1756873 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -678,7 +678,7 @@ int drm_gem_dmabuf_vmap(struct dma_buf *dma_buf, struct iosys_map *map) { struct drm_gem_object *obj = dma_buf->priv;
- return drm_gem_vmap_unlocked(obj, map); + return drm_gem_vmap(obj, map); } EXPORT_SYMBOL(drm_gem_dmabuf_vmap);
@@ -694,7 +694,7 @@ void drm_gem_dmabuf_vunmap(struct dma_buf *dma_buf, struct iosys_map *map) { struct drm_gem_object *obj = dma_buf->priv;
- drm_gem_vunmap_unlocked(obj, map); + drm_gem_vunmap(obj, map); } EXPORT_SYMBOL(drm_gem_dmabuf_vunmap);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c index cc54a5b1d6ae..d1bb6a3760e8 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c @@ -241,8 +241,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
assert_object_held(obj);
- pages = dma_buf_map_attachment_unlocked(obj->base.import_attach, - DMA_BIDIRECTIONAL); + pages = dma_buf_map_attachment_locked(obj->base.import_attach, + DMA_BIDIRECTIONAL); if (IS_ERR(pages)) return PTR_ERR(pages);
@@ -270,8 +270,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj) static void i915_gem_object_put_pages_dmabuf(struct drm_i915_gem_object *obj, struct sg_table *pages) { - dma_buf_unmap_attachment_unlocked(obj->base.import_attach, pages, - DMA_BIDIRECTIONAL); + dma_buf_unmap_attachment_locked(obj->base.import_attach, pages, + DMA_BIDIRECTIONAL); }
static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = { diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 9ab09569dec1..e7a6a8d28862 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -46,7 +46,7 @@ struct dma_buf_ops { /** * @attach: * - * This is called from dma_buf_attach() to make sure that a given + * This is called from dma_buf_attach_unlocked() to make sure that a given * &dma_buf_attachment.dev can access the provided &dma_buf. Exporters * which support buffer objects in special locations like VRAM or * device-specific carveout areas should check whether the buffer could @@ -74,7 +74,7 @@ struct dma_buf_ops { /** * @detach: * - * This is called by dma_buf_detach() to release a &dma_buf_attachment. + * This is called by dma_buf_detach_unlocked() to release a &dma_buf_attachment. * Provided so that exporters can clean up any housekeeping for an * &dma_buf_attachment. * @@ -94,7 +94,7 @@ struct dma_buf_ops { * exclusive with @cache_sgt_mapping. * * This is called automatically for non-dynamic importers from - * dma_buf_attach(). + * dma_buf_attach_unlocked(). * * Note that similar to non-dynamic exporters in their @map_dma_buf * callback the driver must guarantee that the memory is available for @@ -124,8 +124,8 @@ struct dma_buf_ops { /** * @map_dma_buf: * - * This is called by dma_buf_map_attachment() and is used to map a - * shared &dma_buf into device address space, and it is mandatory. It + * This is called by dma_buf_map_attachment_locked() and is used to map + * a shared &dma_buf into device address space, and it is mandatory. It * can only be called if @attach has been called successfully. * * This call may sleep, e.g. when the backing storage first needs to be @@ -181,8 +181,8 @@ struct dma_buf_ops { /** * @unmap_dma_buf: * - * This is called by dma_buf_unmap_attachment() and should unmap and - * release the &sg_table allocated in @map_dma_buf, and it is mandatory. + * This is called by dma_buf_unmap_attachment_locked() and should unmap + * and release the &sg_table allocated in @map_dma_buf, and it is mandatory. * For static dma_buf handling this might also unpin the backing * storage if this is the last mapping of the DMA buffer. */ @@ -509,10 +509,10 @@ struct dma_buf_attach_ops { * and its user device(s). The list contains one attachment struct per device * attached to the buffer. * - * An attachment is created by calling dma_buf_attach(), and released again by - * calling dma_buf_detach(). The DMA mapping itself needed to initiate a - * transfer is created by dma_buf_map_attachment() and freed again by calling - * dma_buf_unmap_attachment(). + * An attachment is created by calling dma_buf_attach_unlocked(), and released + * again by calling dma_buf_detach_unlocked(). The DMA mapping itself needed to + * initiate a transfer is created by dma_buf_map_attachment_locked() and freed + * again by calling dma_buf_unmap_attachment_locked(). */ struct dma_buf_attachment { struct dma_buf *dmabuf; @@ -626,6 +626,12 @@ void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *, struct sg_table *, enum dma_data_direction);
+struct sg_table *dma_buf_map_attachment_locked(struct dma_buf_attachment *, + enum dma_data_direction); +void dma_buf_unmap_attachment_locked(struct dma_buf_attachment *attach, + struct sg_table *sg_table, + enum dma_data_direction direction); + void dma_buf_move_notify(struct dma_buf *dma_buf); int dma_buf_begin_cpu_access(struct dma_buf *dma_buf, enum dma_data_direction dir);