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

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Message-ID: <CA+wgaPPSO1f=c+jYWqisNy_e8hxuxcr0VtpJcWe+FnKGyC2ZKg@mail.gmail.com>
Date:   Wed, 5 Jan 2022 10:38:02 -0800
From:   Hridya Valsaraju <hridya@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
        john.stultz@...aro.org, surenb@...gle.com, kaleshsingh@...gle.com,
        tjmercier@...gle.com, keescook@...gle.com
Subject: Re: [PATCH] dma-buf: Move sysfs work out of DMA-BUF export/release path

On Wed, Jan 5, 2022 at 7:13 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> 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@...gle.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@...uxfoundation.org>

Thank you for the review Greg :)