[Linaro-mm-sig] Re: [PATCH V2] dmabuf: ensure unique directory name for dmabuf stats

On Tue, May 10, 2022 at 7:07 AM Charan Teja Kalla quic_charante@quicinc.com wrote:

The dmabuf file uses get_next_ino()(through dma_buf_getfile() -> alloc_anon_inode()) to get an inode number and uses the same as a directory name under /sys/kernel/dmabuf/buffers/<ino>. This directory is used to collect the dmabuf stats and it is created through dma_buf_stats_setup(). At current, failure to create this directory entry can make the dma_buf_export() to fail.

Now, as the get_next_ino() can definitely give a repetitive inode no causing the directory entry creation to fail with -EEXIST. This is a problem on the systems where dmabuf stats functionality is enabled on the production builds can make the dma_buf_export(), though the dmabuf memory is allocated successfully, to fail just because it couldn't create stats entry.

This issue we are able to see on the snapdragon system within 13 days where there already exists a directory with inode no "122602" so dma_buf_stats_setup() failed with -EEXIST as it is trying to create the same directory entry.

To make the directory entry as unique, append the unique_id for every inode. With this change the stats directory entries will be in the format of: /sys/kernel/dmabuf/buffers/<inode_number-unique_id>.

Signed-off-by: Charan Teja Kalla quic_charante@quicinc.com

Changes in V2: -- Used the atomic64_t variable to generate a unique_id to be appended to inode to have an unique directory with name <inode_number-unique_id> -- Suggested by christian -- Updated the ABI documentation -- Identified by Greg. -- Massaged the commit log.

Changes in V1: -- Used the inode->i_ctime->tv_secs as an id appended to inode to create the unique directory with name <inode_number-time_in_secs>. -- https://lore.kernel.org/all/1652178212-22383-1-git-send-email-quic_charante@...

Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers | 10 +++++----- drivers/dma-buf/Kconfig | 6 +++--- drivers/dma-buf/dma-buf-sysfs-stats.c | 8 +++++--- 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers index 5d3bc99..9fffbd3 100644 --- a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers +++ b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers @@ -4,19 +4,19 @@ KernelVersion: v5.13 Contact: Hridya Valsaraju hridya@google.com Description: The /sys/kernel/dmabuf/buffers directory contains a snapshot of the internal state of every DMA-BUF.

•           /sys/kernel/dmabuf/buffers/<inode_number> will contain the
  

•           statistics for the DMA-BUF with the unique inode number
  

•           <inode_number>
  

•           /sys/kernel/dmabuf/buffers/<inode_number-unique_id> will
  

•           contain the statistics for the DMA-BUF with the unique
  

•           pair <inode_number-unique_id>
  

Android userspace does have a dependency on this being an inode number. Or at least, a single unsigned int. Not the end of the world, but still... this will break. https://cs.android.com/android/platform/superproject/+/master:system/memory/...

Users: kernel memory tuning/debugging tools

-What: /sys/kernel/dmabuf/buffers/<inode_number>/exporter_name +What: /sys/kernel/dmabuf/buffers/<inode_number-unique_id>/exporter_name Date: May 2021 KernelVersion: v5.13 Contact: Hridya Valsaraju hridya@google.com Description: This file is read-only and contains the name of the exporter of the DMA-BUF.

-What: /sys/kernel/dmabuf/buffers/<inode_number>/size +What: /sys/kernel/dmabuf/buffers/<inode_number-unique_id>/size Date: May 2021 KernelVersion: v5.13 Contact: Hridya Valsaraju hridya@google.com diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig index 541efe0..5bcbdb1 100644 --- a/drivers/dma-buf/Kconfig +++ b/drivers/dma-buf/Kconfig @@ -81,9 +81,9 @@ menuconfig DMABUF_SYSFS_STATS Choose this option to enable DMA-BUF sysfs statistics in location /sys/kernel/dmabuf/buffers.

•      /sys/kernel/dmabuf/buffers/<inode_number> will contain
  

•      statistics for the DMA-BUF with the unique inode number
  

•      <inode_number>.
  

•      /sys/kernel/dmabuf/buffers/<inode_number-unique_id> will contain
  

•      statistics for the DMA-BUF with the unique pair
  

•      <inode_number-unique_id>.
  
  

source "drivers/dma-buf/heaps/Kconfig"

diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/dma-buf-sysfs-stats.c index 2bba0ba..29e9e23 100644 --- a/drivers/dma-buf/dma-buf-sysfs-stats.c +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c @@ -38,8 +38,8 @@

• The following stats are exposed by the interface:

• • • ``/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name``
• • • ``/sys/kernel/dmabuf/buffers/<inode_number>/size``

• • • ``/sys/kernel/dmabuf/buffers/<inode_number-unique_id>/exporter_name``
• • • ``/sys/kernel/dmabuf/buffers/<inode_number-unique_id>/size``
  • The information in the interface can also be used to derive per-exporter
  • statistics. The data from the interface can be gathered on error conditions

@@ -172,6 +172,7 @@ int dma_buf_stats_setup(struct dma_buf *dmabuf) { struct dma_buf_sysfs_entry *sysfs_entry; int ret;

•   static atomic64_t unique_id = ATOMIC_INIT(0);
  
    if (!dmabuf || !dmabuf->file)
            return -EINVAL;
  

@@ -192,7 +193,8 @@ int dma_buf_stats_setup(struct dma_buf *dmabuf)

    /* create the directory for buffer stats */
    ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype, NULL,

•                              "%lu", file_inode(dmabuf->file)->i_ino);
  

•                              "%lu-%lu", file_inode(dmabuf->file)->i_ino,
  

•                              atomic64_add_return(1, &unique_id));
    if (ret)
            goto err_sysfs_dmabuf;
  
  

-- 2.7.4