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Date:   Tue, 15 Jun 2021 11:49:38 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Hridya Valsaraju <hridya@google.com>
Cc:     daniel@ffwll.ch, Sumit Semwal <sumit.semwal@linaro.org>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
        linux-doc@vger.kernel.org, kernel-team@android.com,
        john.stultz@linaro.org, surenb@google.com,
        kernel test robot <lkp@intel.com>
Subject: Re: [PATCH v6] dmabuf: Add the capability to expose DMA-BUF stats in
 sysfs
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Mail-Followup-To: Hridya Valsaraju <hridya@google.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
        linux-doc@vger.kernel.org, kernel-team@android.com,
        john.stultz@linaro.org, surenb@google.com,
        kernel test robot <lkp@intel.com>
References: <20210603214758.2955251-1-hridya@google.com>
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On Thu, Jun 03, 2021 at 02:47:51PM -0700, Hridya Valsaraju wrote:
> Overview
> ========
> The patch adds DMA-BUF statistics to /sys/kernel/dmabuf/buffers. It
> allows statistics to be enabled for each DMA-BUF in sysfs by enabling
> the config CONFIG_DMABUF_SYSFS_STATS.
> 
> The following stats will be 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>/attachments/<attach_uid>/device
> /sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter
> 
> The inode_number is unique for each DMA-BUF and was added earlier [1]
> in order to allow userspace to track DMA-BUF usage across different
> processes.
> 
> Use Cases
> =========
> The interface provides a way to gather DMA-BUF per-buffer statistics
> from production devices. These statistics will be used to derive DMA-BUF
> per-exporter stats and per-device usage stats for Android Bug reports.
> The corresponding userspace changes can be found at [2].
> Telemetry tools will also capture this information(along with other
> memory metrics) periodically as well as on important events like a
> foreground app kill (which might have been triggered by Low Memory
> Killer). It will also contribute to provide a snapshot of the system
> memory usage on other events such as OOM kills and Application Not
> Responding events.
> 
> Background
> ==========
> Currently, there are two existing interfaces that provide information
> about DMA-BUFs.
> 1) /sys/kernel/debug/dma_buf/bufinfo
> debugfs is however unsuitable to be mounted in production systems and
> cannot be considered as an alternative to the sysfs interface being
> proposed.
> 2) proc/<pid>/fdinfo/<fd>
> The proc/<pid>/fdinfo/<fd> files expose information about DMA-BUF fds.
> However, the existing procfs interfaces can only provide information
> about the buffers for which processes hold fds or have the buffers
> mmapped into their address space. Since the procfs interfaces alone
> cannot provide a full picture of all DMA-BUFs in the system, there is
> the need for an alternate interface to provide this information on
> production systems.
> 
> The patch contains the following major improvements over v1:
> 1) Each attachment is represented by its own directory to allow creating
> a symlink to the importing device and to also provide room for future
> expansion.
> 2) The number of distinct mappings of each attachment is exposed in a
> separate file.
> 3) The per-buffer statistics are now in /sys/kernel/dmabuf/buffers
> inorder to make the interface expandable in future.
> 
> All of the improvements above are based on suggestions/feedback from
> Daniel Vetter and Christian K?nig.
> 
> A shell script that can be run on a classic Linux environment to read
> out the DMA-BUF statistics can be found at [3](suggested by John
> Stultz).
> 
> [1]: https://lore.kernel.org/patchwork/patch/1088791/
> [2]: https://android-review.googlesource.com/q/topic:%22dmabuf-sysfs%22+(status:open%20OR%20status:merged)
> [3]: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1549734
> 
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Hridya Valsaraju <hridya@google.com>
> Reported-by: kernel test robot <lkp@intel.com>
> ---
> 
> Hello Daniel,
> 
> I have added the documentation as a DOC: overview section in the
> dma-buf-sysfs-stats.c file as per your suggestion. Please do take a look
> when you get a chance. Thanks in advance!
> 
> Regards,
> Hridya
> 
> Change in v6:
> -Moved documentation content from Documentation/driver-api/dma-buf.rst
> to drivers/dma-buf/dma-buf-sysfs-stats.c as a DOC section and linked to
> it from Documentation/driver-api/dma-buf.rst. Based on feedback from
> Daniel Vetter.
> 
> Change in v5:
> -Added a section on DMA-BUF statistics to
> Documentation/driver-api/dma-buf.rst. Organized the commit message to
> clearly state the need for the new interface and provide the
> background on why the existing means of DMA-BUF accounting will not
> suffice. Based on feedback from Daniel Vetter.
> 
> Changes in v4:
> -Suppress uevents from kset creation to avoid waking up uevent listeners
> on DMA-BUF export/release.
> 
> Changes in v3:
> -Fix a warning reported by the kernel test robot.
> 
> Changes in v2:
> -Move statistics to /sys/kernel/dmabuf/buffers in oder to allow addition
> of other DMA-BUF-related sysfs stats in future. Based on feedback from
> Daniel Vetter.
> -Each attachment has its own directory to represent attached devices as
> symlinks and to introduce map_count as a separate file. Based on
> feedback from Daniel Vetter and Christian K?nig. Thank you both!
> -Commit messages updated to point to userspace code in AOSP that will
> read the DMA-BUF sysfs stats.

Pushed to drm-misc-next, thanks for your work. I think the timing just
conspired that this might miss the next merge window though :-/
-Daniel

> 
>  .../ABI/testing/sysfs-kernel-dmabuf-buffers   |  52 +++
>  Documentation/driver-api/dma-buf.rst          |   5 +
>  drivers/dma-buf/Kconfig                       |  11 +
>  drivers/dma-buf/Makefile                      |   1 +
>  drivers/dma-buf/dma-buf-sysfs-stats.c         | 337 ++++++++++++++++++
>  drivers/dma-buf/dma-buf-sysfs-stats.h         |  62 ++++
>  drivers/dma-buf/dma-buf.c                     |  37 ++
>  include/linux/dma-buf.h                       |  20 ++
>  8 files changed, 525 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
>  create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.c
>  create mode 100644 drivers/dma-buf/dma-buf-sysfs-stats.h
> 
> diff --git a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> new file mode 100644
> index 000000000000..a243984ed420
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> @@ -0,0 +1,52 @@
> +What:		/sys/kernel/dmabuf/buffers
> +Date:		May 2021
> +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>
> +Users:		kernel memory tuning/debugging tools
> +
> +What:		/sys/kernel/dmabuf/buffers/<inode_number>/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
> +Date:		May 2021
> +KernelVersion:	v5.13
> +Contact:	Hridya Valsaraju <hridya@google.com>
> +Description:	This file is read-only and specifies the size of the DMA-BUF in
> +		bytes.
> +
> +What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments
> +Date:		May 2021
> +KernelVersion:	v5.13
> +Contact:	Hridya Valsaraju <hridya@google.com>
> +Description:	This directory will contain subdirectories representing every
> +		attachment of the DMA-BUF.
> +
> +What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>
> +Date:		May 2021
> +KernelVersion:	v5.13
> +Contact:	Hridya Valsaraju <hridya@google.com>
> +Description:	This directory will contain information on the attached device
> +		and the number of current distinct device mappings.
> +
> +What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/device
> +Date:		May 2021
> +KernelVersion:	v5.13
> +Contact:	Hridya Valsaraju <hridya@google.com>
> +Description:	This file is read-only and is a symlink to the attached device's
> +		sysfs entry.
> +
> +What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/map_counter
> +Date:		May 2021
> +KernelVersion:	v5.13
> +Contact:	Hridya Valsaraju <hridya@google.com>
> +Description:	This file is read-only and contains a map_counter indicating the
> +		number of distinct device mappings of the attachment.
> diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst
> index 7f37ec30d9fd..d47a429dc549 100644
> --- a/Documentation/driver-api/dma-buf.rst
> +++ b/Documentation/driver-api/dma-buf.rst
> @@ -106,6 +106,11 @@ Implicit Fence Poll Support
>  .. kernel-doc:: drivers/dma-buf/dma-buf.c
>     :doc: implicit fence polling
>  
> +DMA-BUF statistics
> +~~~~~~~~~~~~~~~~~~
> +.. kernel-doc:: drivers/dma-buf/dma-buf-sysfs-stats.c
> +   :doc: overview
> +
>  Kernel Functions and Structures Reference
>  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  
> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index 4e16c71c24b7..9561e3d2d428 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -72,6 +72,17 @@ menuconfig DMABUF_HEAPS
>  	  allows userspace to allocate dma-bufs that can be shared
>  	  between drivers.
>  
> +menuconfig DMABUF_SYSFS_STATS
> +	bool "DMA-BUF sysfs statistics"
> +	select DMA_SHARED_BUFFER
> +	help
> +	   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>.
> +
>  source "drivers/dma-buf/heaps/Kconfig"
>  
>  endmenu
> diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
> index 995e05f609ff..40d81f23cacf 100644
> --- a/drivers/dma-buf/Makefile
> +++ b/drivers/dma-buf/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_DMABUF_HEAPS)	+= heaps/
>  obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
>  obj-$(CONFIG_SW_SYNC)		+= sw_sync.o sync_debug.o
>  obj-$(CONFIG_UDMABUF)		+= udmabuf.o
> +obj-$(CONFIG_DMABUF_SYSFS_STATS) += dma-buf-sysfs-stats.o
>  
>  dmabuf_selftests-y := \
>  	selftest.o \
> diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/dma-buf-sysfs-stats.c
> new file mode 100644
> index 000000000000..a2638e84199c
> --- /dev/null
> +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c
> @@ -0,0 +1,337 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * DMA-BUF sysfs statistics.
> + *
> + * Copyright (C) 2021 Google LLC.
> + */
> +
> +#include <linux/dma-buf.h>
> +#include <linux/dma-resv.h>
> +#include <linux/kobject.h>
> +#include <linux/printk.h>
> +#include <linux/slab.h>
> +#include <linux/sysfs.h>
> +
> +#include "dma-buf-sysfs-stats.h"
> +
> +#define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_buf_sysfs_entry, kobj)
> +
> +/**
> + * DOC: overview
> + *
> + * ``/sys/kernel/debug/dma_buf/bufinfo`` provides an overview of every DMA-BUF
> + * in the system. However, since debugfs is not safe to be mounted in
> + * production, procfs and sysfs can be used to gather DMA-BUF statistics on
> + * production systems.
> + *
> + * The ``/proc/<pid>/fdinfo/<fd>`` files in procfs can be used to gather
> + * information about DMA-BUF fds. Detailed documentation about the interface
> + * is present in Documentation/filesystems/proc.rst.
> + *
> + * Unfortunately, the existing procfs interfaces can only provide information
> + * about the DMA-BUFs for which processes hold fds or have the buffers mmapped
> + * into their address space. This necessitated the creation of the DMA-BUF sysfs
> + * statistics interface to provide per-buffer information on production systems.
> + *
> + * The interface at ``/sys/kernel/dma-buf/buffers`` exposes information about
> + * every DMA-BUF when ``CONFIG_DMABUF_SYSFS_STATS`` is enabled.
> + *
> + * 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>/attachments/<attach_uid>/device``
> + * * ``/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter``
> + *
> + * The information in the interface can also be used to derive per-exporter and
> + * per-device usage statistics. The data from the interface can be gathered
> + * on error conditions or other important events to provide a snapshot of
> + * DMA-BUF usage. It can also be collected periodically by telemetry to monitor
> + * various metrics.
> + *
> + * Detailed documentation about the interface is present in
> + * Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers.
> + */
> +
> +struct dma_buf_stats_attribute {
> +	struct attribute attr;
> +	ssize_t (*show)(struct dma_buf *dmabuf,
> +			struct dma_buf_stats_attribute *attr, char *buf);
> +};
> +#define to_dma_buf_stats_attr(x) container_of(x, struct dma_buf_stats_attribute, attr)
> +
> +static ssize_t dma_buf_stats_attribute_show(struct kobject *kobj,
> +					    struct attribute *attr,
> +					    char *buf)
> +{
> +	struct dma_buf_stats_attribute *attribute;
> +	struct dma_buf_sysfs_entry *sysfs_entry;
> +	struct dma_buf *dmabuf;
> +
> +	attribute = to_dma_buf_stats_attr(attr);
> +	sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
> +	dmabuf = sysfs_entry->dmabuf;
> +
> +	if (!dmabuf || !attribute->show)
> +		return -EIO;
> +
> +	return attribute->show(dmabuf, attribute, buf);
> +}
> +
> +static const struct sysfs_ops dma_buf_stats_sysfs_ops = {
> +	.show = dma_buf_stats_attribute_show,
> +};
> +
> +static ssize_t exporter_name_show(struct dma_buf *dmabuf,
> +				  struct dma_buf_stats_attribute *attr,
> +				  char *buf)
> +{
> +	return sysfs_emit(buf, "%s\n", dmabuf->exp_name);
> +}
> +
> +static ssize_t size_show(struct dma_buf *dmabuf,
> +			 struct dma_buf_stats_attribute *attr,
> +			 char *buf)
> +{
> +	return sysfs_emit(buf, "%zu\n", dmabuf->size);
> +}
> +
> +static struct dma_buf_stats_attribute exporter_name_attribute =
> +	__ATTR_RO(exporter_name);
> +static struct dma_buf_stats_attribute size_attribute = __ATTR_RO(size);
> +
> +static struct attribute *dma_buf_stats_default_attrs[] = {
> +	&exporter_name_attribute.attr,
> +	&size_attribute.attr,
> +	NULL,
> +};
> +ATTRIBUTE_GROUPS(dma_buf_stats_default);
> +
> +static void dma_buf_sysfs_release(struct kobject *kobj)
> +{
> +	struct dma_buf_sysfs_entry *sysfs_entry;
> +
> +	sysfs_entry = to_dma_buf_entry_from_kobj(kobj);
> +	kfree(sysfs_entry);
> +}
> +
> +static struct kobj_type dma_buf_ktype = {
> +	.sysfs_ops = &dma_buf_stats_sysfs_ops,
> +	.release = dma_buf_sysfs_release,
> +	.default_groups = dma_buf_stats_default_groups,
> +};
> +
> +#define to_dma_buf_attach_entry_from_kobj(x) container_of(x, struct dma_buf_attach_sysfs_entry, kobj)
> +
> +struct dma_buf_attach_stats_attribute {
> +	struct attribute attr;
> +	ssize_t (*show)(struct dma_buf_attach_sysfs_entry *sysfs_entry,
> +			struct dma_buf_attach_stats_attribute *attr, char *buf);
> +};
> +#define to_dma_buf_attach_stats_attr(x) container_of(x, struct dma_buf_attach_stats_attribute, attr)
> +
> +static ssize_t dma_buf_attach_stats_attribute_show(struct kobject *kobj,
> +						   struct attribute *attr,
> +						   char *buf)
> +{
> +	struct dma_buf_attach_stats_attribute *attribute;
> +	struct dma_buf_attach_sysfs_entry *sysfs_entry;
> +
> +	attribute = to_dma_buf_attach_stats_attr(attr);
> +	sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
> +
> +	if (!attribute->show)
> +		return -EIO;
> +
> +	return attribute->show(sysfs_entry, attribute, buf);
> +}
> +
> +static const struct sysfs_ops dma_buf_attach_stats_sysfs_ops = {
> +	.show = dma_buf_attach_stats_attribute_show,
> +};
> +
> +static ssize_t map_counter_show(struct dma_buf_attach_sysfs_entry *sysfs_entry,
> +				struct dma_buf_attach_stats_attribute *attr,
> +				char *buf)
> +{
> +	return sysfs_emit(buf, "%u\n", sysfs_entry->map_counter);
> +}
> +
> +static struct dma_buf_attach_stats_attribute map_counter_attribute =
> +	__ATTR_RO(map_counter);
> +
> +static struct attribute *dma_buf_attach_stats_default_attrs[] = {
> +	&map_counter_attribute.attr,
> +	NULL,
> +};
> +ATTRIBUTE_GROUPS(dma_buf_attach_stats_default);
> +
> +static void dma_buf_attach_sysfs_release(struct kobject *kobj)
> +{
> +	struct dma_buf_attach_sysfs_entry *sysfs_entry;
> +
> +	sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
> +	kfree(sysfs_entry);
> +}
> +
> +static struct kobj_type dma_buf_attach_ktype = {
> +	.sysfs_ops = &dma_buf_attach_stats_sysfs_ops,
> +	.release = dma_buf_attach_sysfs_release,
> +	.default_groups = dma_buf_attach_stats_default_groups,
> +};
> +
> +void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach)
> +{
> +	struct dma_buf_attach_sysfs_entry *sysfs_entry;
> +
> +	sysfs_entry = attach->sysfs_entry;
> +	if (!sysfs_entry)
> +		return;
> +
> +	sysfs_delete_link(&sysfs_entry->kobj, &attach->dev->kobj, "device");
> +
> +	kobject_del(&sysfs_entry->kobj);
> +	kobject_put(&sysfs_entry->kobj);
> +}
> +
> +int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> +			       unsigned int uid)
> +{
> +	struct dma_buf_attach_sysfs_entry *sysfs_entry;
> +	int ret;
> +	struct dma_buf *dmabuf;
> +
> +	if (!attach)
> +		return -EINVAL;
> +
> +	dmabuf = attach->dmabuf;
> +
> +	sysfs_entry = kzalloc(sizeof(struct dma_buf_attach_sysfs_entry),
> +			      GFP_KERNEL);
> +	if (!sysfs_entry)
> +		return -ENOMEM;
> +
> +	sysfs_entry->kobj.kset = dmabuf->sysfs_entry->attach_stats_kset;
> +
> +	attach->sysfs_entry = sysfs_entry;
> +
> +	ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_attach_ktype,
> +				   NULL, "%u", uid);
> +	if (ret)
> +		goto kobj_err;
> +
> +	ret = sysfs_create_link(&sysfs_entry->kobj, &attach->dev->kobj,
> +				"device");
> +	if (ret)
> +		goto link_err;
> +
> +	return 0;
> +
> +link_err:
> +	kobject_del(&sysfs_entry->kobj);
> +kobj_err:
> +	kobject_put(&sysfs_entry->kobj);
> +	attach->sysfs_entry = NULL;
> +
> +	return ret;
> +}
> +void dma_buf_stats_teardown(struct dma_buf *dmabuf)
> +{
> +	struct dma_buf_sysfs_entry *sysfs_entry;
> +
> +	sysfs_entry = dmabuf->sysfs_entry;
> +	if (!sysfs_entry)
> +		return;
> +
> +	kset_unregister(sysfs_entry->attach_stats_kset);
> +	kobject_del(&sysfs_entry->kobj);
> +	kobject_put(&sysfs_entry->kobj);
> +}
> +
> +
> +/* Statistics files do not need to send uevents. */
> +static int dmabuf_sysfs_uevent_filter(struct kset *kset, struct kobject *kobj)
> +{
> +	return 0;
> +}
> +
> +static const struct kset_uevent_ops dmabuf_sysfs_no_uevent_ops = {
> +	.filter = dmabuf_sysfs_uevent_filter,
> +};
> +
> +static struct kset *dma_buf_stats_kset;
> +static struct kset *dma_buf_per_buffer_stats_kset;
> +int dma_buf_init_sysfs_statistics(void)
> +{
> +	dma_buf_stats_kset = kset_create_and_add("dmabuf",
> +						 &dmabuf_sysfs_no_uevent_ops,
> +						 kernel_kobj);
> +	if (!dma_buf_stats_kset)
> +		return -ENOMEM;
> +
> +	dma_buf_per_buffer_stats_kset = kset_create_and_add("buffers",
> +							    &dmabuf_sysfs_no_uevent_ops,
> +							    &dma_buf_stats_kset->kobj);
> +	if (!dma_buf_per_buffer_stats_kset) {
> +		kset_unregister(dma_buf_stats_kset);
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +
> +void dma_buf_uninit_sysfs_statistics(void)
> +{
> +	kset_unregister(dma_buf_per_buffer_stats_kset);
> +	kset_unregister(dma_buf_stats_kset);
> +}
> +
> +int dma_buf_stats_setup(struct dma_buf *dmabuf)
> +{
> +	struct dma_buf_sysfs_entry *sysfs_entry;
> +	int ret;
> +	struct kset *attach_stats_kset;
> +
> +	if (!dmabuf || !dmabuf->file)
> +		return -EINVAL;
> +
> +	if (!dmabuf->exp_name) {
> +		pr_err("exporter name must not be empty if stats needed\n");
> +		return -EINVAL;
> +	}
> +
> +	sysfs_entry = kzalloc(sizeof(struct dma_buf_sysfs_entry), GFP_KERNEL);
> +	if (!sysfs_entry)
> +		return -ENOMEM;
> +
> +	sysfs_entry->kobj.kset = dma_buf_per_buffer_stats_kset;
> +	sysfs_entry->dmabuf = dmabuf;
> +
> +	dmabuf->sysfs_entry = sysfs_entry;
> +
> +	/* 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);
> +	if (ret)
> +		goto err_sysfs_dmabuf;
> +
> +	/* create the directory for attachment stats */
> +	attach_stats_kset = kset_create_and_add("attachments",
> +						&dmabuf_sysfs_no_uevent_ops,
> +						&sysfs_entry->kobj);
> +	if (!attach_stats_kset) {
> +		ret = -ENOMEM;
> +		goto err_sysfs_attach;
> +	}
> +
> +	sysfs_entry->attach_stats_kset = attach_stats_kset;
> +
> +	return 0;
> +
> +err_sysfs_attach:
> +	kobject_del(&sysfs_entry->kobj);
> +err_sysfs_dmabuf:
> +	kobject_put(&sysfs_entry->kobj);
> +	dmabuf->sysfs_entry = NULL;
> +	return ret;
> +}
> diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.h b/drivers/dma-buf/dma-buf-sysfs-stats.h
> new file mode 100644
> index 000000000000..5f4703249117
> --- /dev/null
> +++ b/drivers/dma-buf/dma-buf-sysfs-stats.h
> @@ -0,0 +1,62 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * DMA-BUF sysfs statistics.
> + *
> + * Copyright (C) 2021 Google LLC.
> + */
> +
> +#ifndef _DMA_BUF_SYSFS_STATS_H
> +#define _DMA_BUF_SYSFS_STATS_H
> +
> +#ifdef CONFIG_DMABUF_SYSFS_STATS
> +
> +int dma_buf_init_sysfs_statistics(void);
> +void dma_buf_uninit_sysfs_statistics(void);
> +
> +int dma_buf_stats_setup(struct dma_buf *dmabuf);
> +int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> +			       unsigned int uid);
> +static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> +						       int delta)
> +{
> +	struct dma_buf_attach_sysfs_entry *entry = attach->sysfs_entry;
> +
> +	entry->map_counter += delta;
> +}
> +void dma_buf_stats_teardown(struct dma_buf *dmabuf);
> +void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach);
> +static inline unsigned int dma_buf_update_attach_uid(struct dma_buf *dmabuf)
> +{
> +	struct dma_buf_sysfs_entry *entry = dmabuf->sysfs_entry;
> +
> +	return entry->attachment_uid++;
> +}
> +#else
> +
> +static inline int dma_buf_init_sysfs_statistics(void)
> +{
> +	return 0;
> +}
> +
> +static inline void dma_buf_uninit_sysfs_statistics(void) {}
> +
> +static inline int dma_buf_stats_setup(struct dma_buf *dmabuf)
> +{
> +	return 0;
> +}
> +static inline int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> +					     unsigned int uid)
> +{
> +	return 0;
> +}
> +
> +static inline void dma_buf_stats_teardown(struct dma_buf *dmabuf) {}
> +static inline void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach) {}
> +static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> +						       int delta) {}
> +static inline unsigned int dma_buf_update_attach_uid(struct dma_buf *dmabuf)
> +{
> +	return 0;
> +}
> +#endif
> +#endif // _DMA_BUF_SYSFS_STATS_H
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index f264b70c383e..184dd7acb1ed 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -29,6 +29,8 @@
>  #include <uapi/linux/dma-buf.h>
>  #include <uapi/linux/magic.h>
>  
> +#include "dma-buf-sysfs-stats.h"
> +
>  static inline int is_dma_buf_file(struct file *);
>  
>  struct dma_buf_list {
> @@ -79,6 +81,7 @@ static void dma_buf_release(struct dentry *dentry)
>  	if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
>  		dma_resv_fini(dmabuf->resv);
>  
> +	dma_buf_stats_teardown(dmabuf);
>  	module_put(dmabuf->owner);
>  	kfree(dmabuf->name);
>  	kfree(dmabuf);
> @@ -580,6 +583,10 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
>  	file->f_mode |= FMODE_LSEEK;
>  	dmabuf->file = file;
>  
> +	ret = dma_buf_stats_setup(dmabuf);
> +	if (ret)
> +		goto err_sysfs;
> +
>  	mutex_init(&dmabuf->lock);
>  	INIT_LIST_HEAD(&dmabuf->attachments);
>  
> @@ -589,6 +596,14 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
>  
>  	return dmabuf;
>  
> +err_sysfs:
> +	/*
> +	 * Set file->f_path.dentry->d_fsdata to NULL so that when
> +	 * dma_buf_release() gets invoked by dentry_ops, it exits
> +	 * early before calling the release() dma_buf op.
> +	 */
> +	file->f_path.dentry->d_fsdata = NULL;
> +	fput(file);
>  err_dmabuf:
>  	kfree(dmabuf);
>  err_module:
> @@ -723,6 +738,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>  {
>  	struct dma_buf_attachment *attach;
>  	int ret;
> +	unsigned int attach_uid;
>  
>  	if (WARN_ON(!dmabuf || !dev))
>  		return ERR_PTR(-EINVAL);
> @@ -748,8 +764,13 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>  	}
>  	dma_resv_lock(dmabuf->resv, NULL);
>  	list_add(&attach->node, &dmabuf->attachments);
> +	attach_uid = dma_buf_update_attach_uid(dmabuf);
>  	dma_resv_unlock(dmabuf->resv);
>  
> +	ret = dma_buf_attach_stats_setup(attach, attach_uid);
> +	if (ret)
> +		goto err_sysfs;
> +
>  	/* When either the importer or the exporter can't handle dynamic
>  	 * mappings we cache the mapping here to avoid issues with the
>  	 * reservation object lock.
> @@ -776,6 +797,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>  			dma_resv_unlock(attach->dmabuf->resv);
>  		attach->sgt = sgt;
>  		attach->dir = DMA_BIDIRECTIONAL;
> +		dma_buf_update_attachment_map_count(attach, 1 /* delta */);
>  	}
>  
>  	return attach;
> @@ -792,6 +814,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>  	if (dma_buf_is_dynamic(attach->dmabuf))
>  		dma_resv_unlock(attach->dmabuf->resv);
>  
> +err_sysfs:
>  	dma_buf_detach(dmabuf, attach);
>  	return ERR_PTR(ret);
>  }
> @@ -841,6 +864,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>  			dma_resv_lock(attach->dmabuf->resv, NULL);
>  
>  		__unmap_dma_buf(attach, attach->sgt, attach->dir);
> +		dma_buf_update_attachment_map_count(attach, -1 /* delta */);
>  
>  		if (dma_buf_is_dynamic(attach->dmabuf)) {
>  			dma_buf_unpin(attach);
> @@ -854,6 +878,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>  	if (dmabuf->ops->detach)
>  		dmabuf->ops->detach(dmabuf, attach);
>  
> +	dma_buf_attach_stats_teardown(attach);
>  	kfree(attach);
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_detach);
> @@ -993,6 +1018,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>  	}
>  #endif /* CONFIG_DMA_API_DEBUG */
>  
> +	if (!IS_ERR(sg_table))
> +		dma_buf_update_attachment_map_count(attach, 1 /* delta */);
> +
>  	return sg_table;
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
> @@ -1030,6 +1058,8 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>  	if (dma_buf_is_dynamic(attach->dmabuf) &&
>  	    !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
>  		dma_buf_unpin(attach);
> +
> +	dma_buf_update_attachment_map_count(attach, -1 /* delta */);
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
>  
> @@ -1480,6 +1510,12 @@ static inline void dma_buf_uninit_debugfs(void)
>  
>  static int __init dma_buf_init(void)
>  {
> +	int ret;
> +
> +	ret = dma_buf_init_sysfs_statistics();
> +	if (ret)
> +		return ret;
> +
>  	dma_buf_mnt = kern_mount(&dma_buf_fs_type);
>  	if (IS_ERR(dma_buf_mnt))
>  		return PTR_ERR(dma_buf_mnt);
> @@ -1495,5 +1531,6 @@ static void __exit dma_buf_deinit(void)
>  {
>  	dma_buf_uninit_debugfs();
>  	kern_unmount(dma_buf_mnt);
> +	dma_buf_uninit_sysfs_statistics();
>  }
>  __exitcall(dma_buf_deinit);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index efdc56b9d95f..342585bd6dff 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -295,6 +295,9 @@ struct dma_buf_ops {
>   * @poll: for userspace poll support
>   * @cb_excl: for userspace poll support
>   * @cb_shared: for userspace poll support
> + * @sysfs_entry: for exposing information about this buffer in sysfs.
> + * The attachment_uid member of @sysfs_entry is protected by dma_resv lock
> + * and is incremented on each attach.
>   *
>   * This represents a shared buffer, created by calling dma_buf_export(). The
>   * userspace representation is a normal file descriptor, which can be created by
> @@ -330,6 +333,15 @@ struct dma_buf {
>  
>  		__poll_t active;
>  	} cb_excl, cb_shared;
> +#ifdef CONFIG_DMABUF_SYSFS_STATS
> +	/* for sysfs stats */
> +	struct dma_buf_sysfs_entry {
> +		struct kobject kobj;
> +		struct dma_buf *dmabuf;
> +		unsigned int attachment_uid;
> +		struct kset *attach_stats_kset;
> +	} *sysfs_entry;
> +#endif
>  };
>  
>  /**
> @@ -379,6 +391,7 @@ struct dma_buf_attach_ops {
>   * @importer_ops: importer operations for this attachment, if provided
>   * dma_buf_map/unmap_attachment() must be called with the dma_resv lock held.
>   * @importer_priv: importer specific attachment data.
> + * @sysfs_entry: For exposing information about this attachment in sysfs.
>   *
>   * This structure holds the attachment information between the dma_buf buffer
>   * and its user device(s). The list contains one attachment struct per device
> @@ -399,6 +412,13 @@ struct dma_buf_attachment {
>  	const struct dma_buf_attach_ops *importer_ops;
>  	void *importer_priv;
>  	void *priv;
> +#ifdef CONFIG_DMABUF_SYSFS_STATS
> +	/* for sysfs stats */
> +	struct dma_buf_attach_sysfs_entry {
> +		struct kobject kobj;
> +		unsigned int map_counter;
> +	} *sysfs_entry;
> +#endif
>  };
>  
>  /**
> -- 
> 2.32.0.rc1.229.g3e70b5a671-goog
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch