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 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 to the default work
queue. Note that this can lead to a short-term inaccuracy in the dmabuf
sysfs statistics, but this is a tradeoff to prevent the hot path from
being blocked. A work_struct is added to dma_buf to achieve this, but as
it is unioned with the kobject in the sysfs_entry, dma_buf does not
increase in size.
Fixes: bdb8d06dfe ("dmabuf: Add the capability to expose DMA-BUF stats in sysfs")
Originally-by: Hridya Valsaraju <hridya@google.com>
Signed-off-by: T.J. Mercier <tjmercier@google.com>
Bug: 206979019
Bug: 254192604
Link: https://lore.kernel.org/lkml/CABdmKX2dNYhgOYdrrJU6-jt6F=LjCidbKhR6t4F7yaa0SPr+-A@mail.gmail.com/T/
Conflicts:
include/linux/dma-buf.h
1. The android12-5.10 KMI is frozen, and the modification to struct
dma_buf_sysfs_entry in the original patch triggers ABI check
failures. Instead of an anonymous union, use the existing struct
kobject directly as a work_struct with type punning.
(cherry picked from commit fc02d3582a6668bfff235c78f601fca0a15125da
https://android.git.corp.google.com/kernel/common android13-5.10)
Signed-off-by: T.J. Mercier <tjmercier@google.com>
Change-Id: Ic0386849b6b248b0a72215633fc1a50782455bac
5aec776ef8