[PATCH] dma-buf: Move sysfs work out of DMA-BUF export/release path

[Greg Kroah-Hartman]

On Tue, Jan 04, 2022 at 03:51:48PM -0800, Hridya Valsaraju wrote:
> Recently, we noticed an issue where a process went into direct reclaim
> while holding the kernfs rw semaphore for sysfs in write(exclusive)
> mode. This caused processes who were doing DMA-BUF exports and releases
> to go into uninterruptible sleep since they needed to acquire the same
> semaphore for the DMA-BUF sysfs entry creation/deletion. In order to avoid
> blocking DMA-BUF export/release for an indeterminate amount of time
> while another process is holding the sysfs rw semaphore in exclusive
> mode, this patch moves the per-buffer sysfs file creation/deleteion to
> a kthread.
> 
> Fixes: bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-BUF stats in sysfs")
> Signed-off-by: Hridya Valsaraju <hridya at google.com>
> ---
>  drivers/dma-buf/dma-buf-sysfs-stats.c | 343 ++++++++++++++++++++++++--
>  include/linux/dma-buf.h               |  46 ++++
>  2 files changed, 366 insertions(+), 23 deletions(-)

Crazy, but if this works in your testing, it looks ok to me.  Nice work.

Reviewed-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>