From: Charan Teja Kalla quic_charante@quicinc.com
commit 370704e707a5f2d3c9a1d4ed8bd8cd67507d7bb5 upstream.
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 dentry name as unique, use the dmabuf fs specific inode which is based on the simple atomic variable increment. There is tmpfs subsystem too which relies on its own inode generation rather than relying on the get_next_ino() for the same reason of avoiding the duplicate inodes[1].
[1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/patch/?id=e...
Signed-off-by: Charan Teja Kalla quic_charante@quicinc.com Cc: stable@vger.kernel.org # 5.15.x+ Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Reviewed-by: Christian König christian.koenig@amd.com Link: https://patchwork.freedesktop.org/patch/msgid/1652441296-1986-1-git-send-ema... Signed-off-by: Christian König christian.koenig@amd.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/dma-buf/dma-buf.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -436,6 +436,7 @@ static inline int is_dma_buf_file(struct
static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags) { + static atomic64_t dmabuf_inode = ATOMIC64_INIT(0); struct file *file; struct inode *inode = alloc_anon_inode(dma_buf_mnt->mnt_sb);
@@ -445,6 +446,13 @@ static struct file *dma_buf_getfile(stru inode->i_size = dmabuf->size; inode_set_bytes(inode, dmabuf->size);
+ /* + * The ->i_ino acquired from get_next_ino() is not unique thus + * not suitable for using it as dentry name by dmabuf stats. + * Override ->i_ino with the unique and dmabuffs specific + * value. + */ + inode->i_ino = atomic64_add_return(1, &dmabuf_inode); file = alloc_file_pseudo(inode, dma_buf_mnt, "dmabuf", flags, &dma_buf_fops); if (IS_ERR(file))