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SubjectRe: [PATCH] dmabuf: Add the capability to expose DMA-BUF stats in sysfs
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In general a good idea, but I have a few concern/comments here.

Am 10.12.20 um 05:43 schrieb Hridya Valsaraju:
> This patch 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/<inode_number>/exporter_name
> /sys/kernel/dmabuf/<inode_number>/size
> /sys/kernel/dmabuf/<inode_number>/dev_map_info
>
> 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.
>
> Currently, this information is exposed in
> /sys/kernel/debug/dma_buf/bufinfo.
> However, since debugfs is considered unsafe to be mounted in production,
> it is being duplicated in sysfs.

Mhm, this makes it part of the UAPI. What is the justification for this?

In other words do we really need those debug information in a production
environment?

>
> This information is intended to help with root-causing
> low-memory kills and the debugging/analysis of other memory-related issues.
>
> It will also be used to derive DMA-BUF
> per-exporter stats and per-device usage stats for Android Bug reports.
>
> [1]: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fpatchwork%2Fpatch%2F1088791%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C30a0e015502b4d20e18208d89cc63f1a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637431722574983797%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=RdGMvj5VsFUwJcVOuSPaLuAr4eI3CR1YOaznupmpTqg%3D&amp;reserved=0
>
> Signed-off-by: Hridya Valsaraju <hridya@google.com>
> ---
> Documentation/ABI/testing/sysfs-kernel-dmabuf | 32 ++++
> drivers/dma-buf/Kconfig | 11 ++
> drivers/dma-buf/Makefile | 1 +
> drivers/dma-buf/dma-buf-sysfs-stats.c | 162 ++++++++++++++++++
> drivers/dma-buf/dma-buf-sysfs-stats.h | 37 ++++
> drivers/dma-buf/dma-buf.c | 29 ++++
> include/linux/dma-buf.h | 13 ++
> 7 files changed, 285 insertions(+)
> create mode 100644 Documentation/ABI/testing/sysfs-kernel-dmabuf
> 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 b/Documentation/ABI/testing/sysfs-kernel-dmabuf
> new file mode 100644
> index 000000000000..02d407d57aaa
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-kernel-dmabuf
> @@ -0,0 +1,32 @@
> +What: /sys/kernel/dmabuf
> +Date: November 2020
> +KernelVersion: v5.11
> +Contact: Hridya Valsaraju <hridya@google.com>
> +Description: The /sys/kernel/dmabuf directory contains a
> + snapshot of the internal state of every DMA-BUF.
> + /sys/kernel/dmabuf/<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/<inode_number>/exporter_name
> +Date: November 2020
> +KernelVersion: v5.11
> +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/<inode_number>/size
> +Dat: November 2020
> +KernelVersion: v5.11
> +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/<inode_number>/dev_map_info
> +Dat: November 2020
> +KernelVersion: v5.11
> +Contact: Hridya Valsaraju <hridya@google.com>
> +Description: This file is read-only and lists the name of devices currently
> + mapping the DMA-BUF in a space-separated format.
> +
> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index 4f8224a6ac95..2fed26f14548 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -64,6 +64,17 @@ 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.
> +
> + /sys/kernel/dmabuf/<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..bcbef81e0a5f
> --- /dev/null
> +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c
> @@ -0,0 +1,162 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +
> +#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>
> +
> +#define to_dma_buf_entry_from_kobj(x) container_of(x, struct dma_buf_sysfs_entry, kobj)
> +
> +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 ssize_t dev_map_info_show(struct dma_buf *dmabuf,
> + struct dma_buf_stats_attribute *attr,
> + char *buf)
> +{
> + ssize_t ret;
> + struct dma_buf_attachment *attachment;
> +
> + ret = dma_resv_lock_interruptible(dmabuf->resv, NULL);
> + if (ret)
> + return ret;
> +
> + list_for_each_entry(attachment, &dmabuf->attachments, node) {
> + if (attachment->map_counter) {
> + ret += sysfs_emit_at(buf, ret, "%s ",
> + dev_name(attachment->dev));
> + }

Why do you emit this only when there is a mapping? It is perfectly valid
and current practice that importers map things only on first use.

The number of mapping is in general rather interesting, but I would just
print that together with the importer name.

And BTW I would rename the dev_map_info to something like "attachments".

Regards,
Christian.

> + }
> + dma_resv_unlock(dmabuf->resv);
> +
> + ret += sysfs_emit_at(buf, ret, "\n");
> + return ret;
> +}
> +
> +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 dma_buf_stats_attribute dev_map_info_attribute =
> + __ATTR_RO(dev_map_info);
> +
> +static struct attribute *dma_buf_stats_default_attrs[] = {
> + &exporter_name_attribute.attr,
> + &size_attribute.attr,
> + &dev_map_info_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,
> +};
> +
> +void dma_buf_sysfs_free(struct dma_buf *dmabuf)
> +{
> + struct dma_buf_sysfs_entry *sysfs_entry;
> +
> + sysfs_entry = dmabuf->sysfs_entry;
> + if (!sysfs_entry)
> + return;
> +
> + kobject_del(&sysfs_entry->kobj);
> + kobject_put(&sysfs_entry->kobj);
> +}
> +
> +static struct kset *dma_buf_stats_kset;
> +int dma_buf_init_sysfs_statistics(void)
> +{
> + dma_buf_stats_kset = kset_create_and_add("dmabuf", NULL, kernel_kobj);
> + if (!dma_buf_stats_kset)
> + return -ENOMEM;
> +
> + return 0;
> +}
> +
> +void dma_buf_uninit_sysfs_statistics(void)
> +{
> + kset_unregister(dma_buf_stats_kset);
> +}
> +
> +int dma_buf_init_stats_kobj(struct dma_buf *dmabuf)
> +{
> + struct dma_buf_sysfs_entry *sysfs_entry;
> + int ret;
> +
> + 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_stats_kset;
> + sysfs_entry->dmabuf = dmabuf;
> +
> + dmabuf->sysfs_entry = sysfs_entry;
> +
> + ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_ktype, NULL,
> + "%lu", file_inode(dmabuf->file)->i_ino);
> + if (ret)
> + kobject_put(&sysfs_entry->kobj);
> +
> + 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..42fae7d1b11f
> --- /dev/null
> +++ b/drivers/dma-buf/dma-buf-sysfs-stats.h
> @@ -0,0 +1,37 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#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_init_stats_kobj(struct dma_buf *dmabuf);
> +static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> + int delta)
> +{
> + attach->map_counter += delta;
> +}
> +void dma_buf_sysfs_free(struct dma_buf *dmabuf);
> +
> +#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_init_stats_kobj(struct dma_buf *dmabuf)
> +{
> + return 0;
> +}
> +static inline void dma_buf_sysfs_free(struct dma_buf *dmabuf) {}
> +static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> + int delta) {}
> +
> +#endif
> +#endif // _DMA_BUF_SYSFS_STATS_H
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index e63684d4cd90..e93df0069bf8 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 {
> @@ -83,6 +85,7 @@ static void dma_buf_release(struct dentry *dentry)
> if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
> dma_resv_fini(dmabuf->resv);
>
> + dma_buf_sysfs_free(dmabuf);
> module_put(dmabuf->owner);
> kfree(dmabuf->name);
> kfree(dmabuf);
> @@ -566,6 +569,10 @@ 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_init_stats_kobj(dmabuf);
> + if (ret)
> + goto err_sysfs;
> +
> mutex_init(&dmabuf->lock);
> INIT_LIST_HEAD(&dmabuf->attachments);
>
> @@ -575,6 +582,14 @@ 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:
> @@ -732,6 +747,7 @@ 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;
> @@ -786,6 +802,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> dma_resv_lock(attach->dmabuf->resv, NULL);
>
> dmabuf->ops->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);
> @@ -925,6 +942,9 @@ 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);
> @@ -962,6 +982,8 @@ 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);
>
> @@ -1399,6 +1421,12 @@ 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);
> @@ -1414,5 +1442,6 @@ 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 cf72699cb2bc..f5cab13afdfc 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -294,6 +294,7 @@ 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
> *
> * This represents a shared buffer, created by calling dma_buf_export(). The
> * userspace representation is a normal file descriptor, which can be created by
> @@ -329,6 +330,13 @@ 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;
> + } *sysfs_entry;
> +#endif
> };
>
> /**
> @@ -378,6 +386,8 @@ 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.
> + * @map_counter: Number of times the buffer has been mapped through this
> + * dma_buf_map_attachment.
> *
> * This structure holds the attachment information between the dma_buf buffer
> * and its user device(s). The list contains one attachment struct per device
> @@ -398,6 +408,9 @@ struct dma_buf_attachment {
> const struct dma_buf_attach_ops *importer_ops;
> void *importer_priv;
> void *priv;
> +#ifdef CONFIG_DMABUF_SYSFS_STATS
> + unsigned int map_counter;
> +#endif
> };
>
> /**

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