[Linaro-mm-sig] Re: [RFC v2 6/6] android: binder: Add a buffer flag to relinquish ownership of fds

On Mon, Feb 14, 2022 at 1:26 PM Todd Kjos tkjos@google.com wrote:

On Fri, Feb 11, 2022 at 8:19 AM T.J. Mercier tjmercier@google.com wrote:

...

This patch introduces a buffer flag BINDER_BUFFER_FLAG_SENDER_NO_NEED that a process sending an fd array to another process over binder IPC can set to relinquish ownership of the fds being sent for memory accounting purposes. If the flag is found to be set during the fd array translation and the fd is for a DMA-BUF, the buffer is uncharged from the sender's cgroup and charged to the receiving process's cgroup instead.

It is up to the sending process to ensure that it closes the fds regardless of whether the transfer failed or succeeded.

Most graphics shared memory allocations in Android are done by the graphics allocator HAL process. On requests from clients, the HAL process allocates memory and sends the fds to the clients over binder IPC. The graphics allocator HAL will not retain any references to the buffers. When the HAL sets the BINDER_BUFFER_FLAG_SENDER_NO_NEED for fd arrays holding DMA-BUF fds, the gpu cgroup controller will be able to correctly charge the buffers to the client processes instead of the graphics allocator HAL.

From: Hridya Valsaraju hridya@google.com Signed-off-by: Hridya Valsaraju hridya@google.com Co-developed-by: T.J. Mercier tjmercier@google.com Signed-off-by: T.J. Mercier tjmercier@google.com

---

changes in v2

• Move dma-buf cgroup charge transfer from a dma_buf_op defined by every

heap to a single dma-buf function for all heaps per Daniel Vetter and Christian König.

drivers/android/binder.c | 26 ++++++++++++++++++++++++++ include/uapi/linux/android/binder.h | 1 + 2 files changed, 27 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 8351c5638880..f50d88ded188 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -42,6 +42,7 @@

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

+#include <linux/dma-buf.h> #include <linux/fdtable.h> #include <linux/file.h> #include <linux/freezer.h> @@ -2482,8 +2483,10 @@ static int binder_translate_fd_array(struct list_head *pf_head,

Is this only needed for the BINDER_TYPE_FDA case (multiple fds)? This never needs to be done in the BINDER_TYPE_FD case (single fd)?

Currently this is the case as there is no user who would benefit from the single fd case. The only known user is the gralloc HAL which always uses BINDER_TYPE_FDA to send dmabufs. I guess we could move the code into binder_translate_fd if we were willing to bring back binder_fd_object's flags field. This looks possible, but I think it'd be a more intrusive change.

...

{ binder_size_t fdi, fd_buf_size; binder_size_t fda_offset;

•   bool transfer_gpu_charge = false;
    const void __user *sender_ufda_base;
    struct binder_proc *proc = thread->proc;
  

•   struct binder_proc *target_proc = t->to_proc;
    int ret;
  
    fd_buf_size = sizeof(u32) * fda->num_fds;
  

@@ -2521,8 +2524,15 @@ static int binder_translate_fd_array(struct list_head *pf_head, if (ret) return ret;

•   if (IS_ENABLED(CONFIG_CGROUP_GPU) &&
  

•           parent->flags & BINDER_BUFFER_FLAG_SENDER_NO_NEED)
  

•           transfer_gpu_charge = true;
  

•   for (fdi = 0; fdi < fda->num_fds; fdi++) {
            u32 fd;
  

•           struct dma_buf *dmabuf;
  

•           struct gpucg *gpucg;
  

•           binder_size_t offset = fda_offset + fdi * sizeof(fd);
            binder_size_t sender_uoffset = fdi * sizeof(fd);
  
  

@@ -2532,6 +2542,22 @@ static int binder_translate_fd_array(struct list_head *pf_head, in_reply_to); if (ret) return ret > 0 ? -EINVAL : ret;

•           if (!transfer_gpu_charge)
  

•                   continue;
  

•           dmabuf = dma_buf_get(fd);
  

•           if (IS_ERR(dmabuf))
  

•                   continue;
  

•           gpucg = gpucg_get(target_proc->tsk);
  

•           ret = dma_buf_charge_transfer(dmabuf, gpucg);
  

•           if (ret) {
  

•                   pr_warn("%d:%d Unable to transfer DMA-BUF fd charge to %d",
  

•                           proc->pid, thread->pid, target_proc->pid);
  

•                   gpucg_put(gpucg);
  

•           }
  

•           dma_buf_put(dmabuf);
    }
    return 0;
  

} diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h index 3246f2c74696..169fd5069a1a 100644 --- a/include/uapi/linux/android/binder.h +++ b/include/uapi/linux/android/binder.h @@ -137,6 +137,7 @@ struct binder_buffer_object {

enum { BINDER_BUFFER_FLAG_HAS_PARENT = 0x01,

•   BINDER_BUFFER_FLAG_SENDER_NO_NEED = 0x02,
  

};

/* struct binder_fd_array_object - object describing an array of fds in a buffer

2.35.1.265.g69c8d7142f-goog