The dma_buf_transfer_charge function provides a way for processes to transfer charge of a buffer to a different cgroup. This is essential for the cases where a central allocator process does allocations for various subsystems, hands over the fd to the client who requested the memory, and drops all references to the allocated memory.
Signed-off-by: T.J. Mercier tjmercier@google.com --- drivers/dma-buf/dma-buf.c | 56 ++++++++++++++++++++++++++++++++++++++ include/linux/dma-buf.h | 1 + include/linux/memcontrol.h | 5 ++++ 3 files changed, 62 insertions(+)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index a6a8cb5cb32d..ac3d02a7ecf8 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -11,6 +11,7 @@ * refining of this idea. */
+#include <linux/atomic.h> #include <linux/fs.h> #include <linux/slab.h> #include <linux/dma-buf.h> @@ -1626,6 +1627,61 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map) } EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap_unlocked, DMA_BUF);
+/** + * dma_buf_transfer_charge - Change the cgroup to which the provided dma_buf is charged. + * @dmabuf_file: [in] file for buffer whose charge will be migrated to a different cgroup + * @target: [in] the task_struct of the destination process for the cgroup charge + * + * Only tasks that belong to the same cgroup the buffer is currently charged to + * may call this function, otherwise it will return -EPERM. + * + * Returns 0 on success, or a negative errno code otherwise. + */ +int dma_buf_transfer_charge(struct file *dmabuf_file, struct task_struct *target) +{ + struct mem_cgroup *current_cg, *target_cg; + struct dma_buf *dmabuf; + unsigned int nr_pages; + int ret = 0; + + if (!IS_ENABLED(CONFIG_MEMCG)) + return 0; + + if (WARN_ON(!dmabuf_file) || WARN_ON(!target)) + return -EINVAL; + + if (!is_dma_buf_file(dmabuf_file)) + return -EBADF; + dmabuf = dmabuf_file->private_data; + + nr_pages = PAGE_ALIGN(dmabuf->size) / PAGE_SIZE; + current_cg = mem_cgroup_from_task(current); + target_cg = get_mem_cgroup_from_mm(target->mm); + + if (current_cg == target_cg) + goto skip_transfer; + + if (!mem_cgroup_charge_dmabuf(target_cg, nr_pages, GFP_KERNEL)) { + ret = -ENOMEM; + goto skip_transfer; + } + + if (cmpxchg(&dmabuf->memcg, current_cg, target_cg) != current_cg) { + /* Only the current owner can transfer the charge */ + ret = -EPERM; + mem_cgroup_uncharge_dmabuf(target_cg, nr_pages); + goto skip_transfer; + } + + mem_cgroup_uncharge_dmabuf(current_cg, nr_pages); + mem_cgroup_put(current_cg); /* unref from buffer - buffer keeps new ref to target_cg */ + return 0; + +skip_transfer: + mem_cgroup_put(target_cg); + return ret; +} + #ifdef CONFIG_DEBUG_FS static int dma_buf_debug_show(struct seq_file *s, void *unused) { diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 1f0ffb8e4bf5..f25eb8e60fb2 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -634,4 +634,5 @@ int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map); void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map); int 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); +int dma_buf_transfer_charge(struct file *dmabuf_file, struct task_struct *target); #endif /* __DMA_BUF_H__ */ diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index c10b8565fdbf..009298a446fe 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1335,6 +1335,11 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css) return NULL; }
+static inline struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p) +{ + return NULL; +} + static inline void obj_cgroup_put(struct obj_cgroup *objcg) { }