Message-ID: <s66dyt32ukr37p24zjgbatm6sk5lzw5ujx2n7p2pr2ixrq3jf4@byemjauyp2mv>
Date: Tue, 8 Apr 2025 14:38:44 +0100
From: Adrián Larumbe <adrian.larumbe@...labora.com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Sumit Semwal <sumit.semwal@...aro.org>, 
	Christian König <christian.koenig@....com>, kernel@...labora.com, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v4 4/4] drm/panthor: show device-wide list of DRM GEM
 objects over DebugFS

On 02.04.2025 14:58, Boris Brezillon wrote:
> On Wed,  2 Apr 2025 12:54:29 +0100
> Adrián Larumbe <adrian.larumbe@...labora.com> wrote:
>
> > Add a device DebugFS file that displays a complete list of all the DRM
> > GEM objects that are exposed to UM through a DRM handle.
> >
> > Since leaking object identifiers that might belong to a different NS is
> > inadmissible, this functionality is only made available in debug builds
> > with DEBUGFS support enabled.
> >
> > File format is that of a table, with each entry displaying a variety of
> > fields with information about each GEM object.
> >
> > Each GEM object entry in the file displays the following information
> > fields: Client PID, BO's global name, reference count, BO virtual size,
> > BO resize size, VM address in its DRM-managed range, BO label and a flag
> > bitmask.
> >
> > There's also a kflags field for the type of BO. Bit 0 tells us whether
> > it's a kernel BO, and bit 1 means the BO is mapped onto the FW's address
> > space.
> >
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
> > ---
> >  drivers/gpu/drm/panthor/panthor_device.c |   5 +
> >  drivers/gpu/drm/panthor/panthor_device.h |  11 ++
> >  drivers/gpu/drm/panthor/panthor_drv.c    |  26 ++++
> >  drivers/gpu/drm/panthor/panthor_gem.c    | 149 +++++++++++++++++++++++
> >  drivers/gpu/drm/panthor/panthor_gem.h    |  35 ++++++
> >  5 files changed, 226 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> > index a9da1d1eeb70..b776e1a2e4f3 100644
> > --- a/drivers/gpu/drm/panthor/panthor_device.c
> > +++ b/drivers/gpu/drm/panthor/panthor_device.c
> > @@ -184,6 +184,11 @@ int panthor_device_init(struct panthor_device *ptdev)
> >  	if (ret)
> >  		return ret;
> >
> > +#ifdef CONFIG_DEBUG_FS
> > +	drmm_mutex_init(&ptdev->base, &ptdev->gems.lock);
> > +	INIT_LIST_HEAD(&ptdev->gems.node);
> > +#endif
> > +
> >  	atomic_set(&ptdev->pm.state, PANTHOR_DEVICE_PM_STATE_SUSPENDED);
> >  	p = alloc_page(GFP_KERNEL | __GFP_ZERO);
> >  	if (!p)
> > diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> > index da6574021664..86206a961b38 100644
> > --- a/drivers/gpu/drm/panthor/panthor_device.h
> > +++ b/drivers/gpu/drm/panthor/panthor_device.h
> > @@ -205,6 +205,17 @@ struct panthor_device {
> >
> >  	/** @fast_rate: Maximum device clock frequency. Set by DVFS */
> >  	unsigned long fast_rate;
> > +
> > +#ifdef CONFIG_DEBUG_FS
> > +	/** @gems: Device-wide list of GEM objects owned by at least one file. */
> > +	struct {
> > +		/** @gems.lock: Protects the device-wide list of GEM objects. */
> > +		struct mutex lock;
> > +
> > +		/** @node: Used to keep track of all the device's DRM objects */
> > +		struct list_head node;
> > +	} gems;
> > +#endif
> >  };
> >
> >  struct panthor_gpu_usage {
> > diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> > index d5277284fe27..3e870ed2ad90 100644
> > --- a/drivers/gpu/drm/panthor/panthor_drv.c
> > +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> > @@ -1534,9 +1534,35 @@ static const struct file_operations panthor_drm_driver_fops = {
> >  };
> >
> >  #ifdef CONFIG_DEBUG_FS
> > +static int panthor_gems_show(struct seq_file *m, void *data)
> > +{
> > +	struct drm_info_node *node = m->private;
> > +	struct drm_device *dev = node->minor->dev;
> > +	struct panthor_device *ptdev = container_of(dev, struct panthor_device, base);
> > +
> > +	panthor_gem_debugfs_print_bos(ptdev, m);
> > +
> > +	return 0;
> > +}
> > +
> > +
> > +static struct drm_info_list panthor_debugfs_list[] = {
> > +	{"gems", panthor_gems_show, 0, NULL},
> > +};
> > +
> > +static int panthor_gems_debugfs_init(struct drm_minor *minor)
> > +{
> > +	drm_debugfs_create_files(panthor_debugfs_list,
> > +				 ARRAY_SIZE(panthor_debugfs_list),
> > +				 minor->debugfs_root, minor);
> > +
> > +	return 0;
> > +}
> > +
> >  static void panthor_debugfs_init(struct drm_minor *minor)
> >  {
> >  	panthor_mmu_debugfs_init(minor);
> > +	panthor_gems_debugfs_init(minor);
> >  }
> >  #endif
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> > index 44d027e6d664..2fc87be9b700 100644
> > --- a/drivers/gpu/drm/panthor/panthor_gem.c
> > +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> > @@ -2,6 +2,7 @@
> >  /* Copyright 2019 Linaro, Ltd, Rob Herring <robh@...nel.org> */
> >  /* Copyright 2023 Collabora ltd. */
> >
> > +#include <linux/cleanup.h>
> >  #include <linux/dma-buf.h>
> >  #include <linux/dma-mapping.h>
> >  #include <linux/err.h>
> > @@ -10,14 +11,65 @@
> >  #include <drm/panthor_drm.h>
> >
> >  #include "panthor_device.h"
> > +#include "panthor_fw.h"
> >  #include "panthor_gem.h"
> >  #include "panthor_mmu.h"
> >
> > +#ifdef CONFIG_DEBUG_FS
> > +static void panthor_gem_debugfs_bo_init(struct panthor_gem_object *bo, u32 type_mask)
> > +{
> > +	INIT_LIST_HEAD(&bo->debugfs.node);
>
> This should be called when the GEM object is created, otherwise the
> list_empty() test done in panthor_gem_debugfs_bo_rm() will only work if
> panthor_gem_debugfs_bo_add() is called, and depending on when this
> happens, or whether it happens at all, the error path will do a NULL
> deref.

I'll be moving panthor_gem_debugfs_bo_add() back into panthor_gem_create_object() and
inline panthor_gem_debugfs_bo_init() into it.

> > +
> > +	if (!(type_mask & PANTHOR_BO_FW_MAPPED)) {
> > +		bo->debugfs.creator.tgid = current->group_leader->pid;
> > +		get_task_comm(bo->debugfs.creator.process_name, current->group_leader);
>
> I don't think that's good to assume that FW-mapped BOs have been
> created by the kernel without userspace directly or indirectly asking
> for the allocation. For instance, per-group memory allocated for the
> USER_CS interfaces are indirectly triggered by a GROUP_CREATE ioctl(),
> and should IMO be flagged as being created by the process that
> created the group. Don't we have another way to check if we're called
> from a kernel thread?

True, I completely missed this. I did some research of the kernel API and apparently
is_kthread() might do the job.

> > +	} else {
> > +		bo->debugfs.creator.tgid = 0;
> > +		snprintf(bo->debugfs.creator.process_name,
> > +			 sizeof(bo->debugfs.creator.process_name),
> > +			 "kernel");
> > +	}
> > +
> > +	bo->debugfs.bo_mask = type_mask;
>
> Why not do that directly in panthor_gem_debugfs_bo_add()? The only bits
> that might be useful to do early is the INIT_LIST_HEAD(), and I think
> it can be inlined in panthor_gem_create_object().

I'll be doing in this in the next revision, but because I've no access to the BO
type mask from inside Panthor's drm_driver::gem_create_object() binding, then
I'll have to assign the mask right after the object has been created.

I think this means there might be a short window after the object's been added to
the DebugFS GEMs list in which it could be shown with the kernel mask field still
set to 0, but I guess that's not too important either.

> > +}
> > +
> > +static void panthor_gem_debugfs_bo_add(struct panthor_gem_object *bo, u32 type_mask)
> > +{
> > +	struct panthor_device *ptdev =  container_of(bo->base.base.dev,
> > +						     struct panthor_device, base);
> > +
> > +	panthor_gem_debugfs_bo_init(bo, type_mask);
> > +
> > +	mutex_lock(&ptdev->gems.lock);
> > +	list_add_tail(&bo->debugfs.node, &ptdev->gems.node);
> > +	mutex_unlock(&ptdev->gems.lock);
> > +}
> > +
> > +static void panthor_gem_debugfs_bo_rm(struct panthor_gem_object *bo)
> > +{
> > +	struct panthor_device *ptdev = container_of(bo->base.base.dev,
> > +						    struct panthor_device, base);
> > +
> > +	if (list_empty(&bo->debugfs.node))
> > +		return;
> > +
> > +	mutex_lock(&ptdev->gems.lock);
> > +	list_del_init(&bo->debugfs.node);
> > +	mutex_unlock(&ptdev->gems.lock);
> > +}
> > +
> > +#else
> > +static void panthor_gem_debugfs_bo_add(struct panthor_gem_object *bo, u32 type_mask) {}
> > +static void panthor_gem_debugfs_bo_rm(struct panthor_gem_object *bo) {}
> > +#endif
> > +
> >  static void panthor_gem_free_object(struct drm_gem_object *obj)
> >  {
> >  	struct panthor_gem_object *bo = to_panthor_bo(obj);
> >  	struct drm_gem_object *vm_root_gem = bo->exclusive_vm_root_gem;
> >
> > +	panthor_gem_debugfs_bo_rm(bo);
> > +
> >  	/*
> >  	 * Label might have been allocated with kstrdup_const(),
> >  	 * we need to take that into account when freeing the memory
> > @@ -86,6 +138,7 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
> >  	struct drm_gem_shmem_object *obj;
> >  	struct panthor_kernel_bo *kbo;
> >  	struct panthor_gem_object *bo;
> > +	u32 type_mask = PANTHOR_BO_KERNEL;
> >  	int ret;
> >
> >  	if (drm_WARN_ON(&ptdev->base, !vm))
> > @@ -105,7 +158,12 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
> >  	kbo->obj = &obj->base;
> >  	bo->flags = bo_flags;
> >
> > +	if (vm == panthor_fw_vm(ptdev))
> > +		type_mask |= PANTHOR_BO_FW_MAPPED;
> > +
> >  	panthor_gem_kernel_bo_set_label(kbo, name);
> > +	panthor_gem_debugfs_bo_add(to_panthor_bo(kbo->obj), type_mask);
> > +
> >  	/* The system and GPU MMU page size might differ, which becomes a
> >  	 * problem for FW sections that need to be mapped at explicit address
> >  	 * since our PAGE_SIZE alignment might cover a VA range that's
> > @@ -255,6 +313,8 @@ panthor_gem_create_with_handle(struct drm_file *file,
> >  	/* drop reference from allocate - handle holds it now. */
> >  	drm_gem_object_put(&shmem->base);
> >
> > +	panthor_gem_debugfs_bo_add(bo, 0);
> > +
> >  	return ret;
> >  }
> >
> > @@ -286,3 +346,92 @@ panthor_gem_kernel_bo_set_label(struct panthor_kernel_bo *bo, const char *label)
> >
> >  	panthor_gem_bo_set_label(bo->obj, kstrdup_const(str, GFP_KERNEL));
> >  }
> > +
> > +#ifdef CONFIG_DEBUG_FS
> > +static bool panfrost_gem_print_flag(const char *name,
> > +				    bool is_set,
> > +				    bool other_flags_printed,
> > +				    struct seq_file *m)
> > +{
> > +	if (is_set)
> > +		seq_printf(m, "%s%s", other_flags_printed ? "," : "", name);
> > +
> > +	return is_set | other_flags_printed;
> > +}
> > +
> > +struct gem_size_totals {
> > +	size_t size;
> > +	size_t resident;
> > +	size_t reclaimable;
> > +};
> > +
> > +static void panthor_gem_debugfs_bo_print(struct panthor_gem_object *bo,
> > +					 struct seq_file *m,
> > +					 struct gem_size_totals *totals)
> > +{
> > +	unsigned int refcount = kref_read(&bo->base.base.refcount);
> > +	char creator_info[32] = {};
> > +	bool has_flags = false;
> > +	size_t resident_size;
> > +
> > +	/* Skip BOs being destroyed. */
> > +	if (!refcount)
> > +		return;
> > +
> > +	resident_size = bo->base.pages != NULL ? bo->base.base.size : 0;
> > +
> > +	snprintf(creator_info, sizeof(creator_info),
> > +		 "%s/%d", bo->debugfs.creator.process_name, bo->debugfs.creator.tgid);
> > +	seq_printf(m, "%-32s%-16d%-16d%-16zd%-16zd%-16lx",
> > +		   creator_info,
> > +		   bo->base.base.name,
> > +		   refcount,
> > +		   bo->base.base.size,
> > +		   resident_size,
> > +		   drm_vma_node_start(&bo->base.base.vma_node));
> > +
> > +	seq_puts(m, "(");
> > +	has_flags = panfrost_gem_print_flag("imported", bo->base.base.import_attach != NULL,
> > +					    has_flags, m);
> > +	has_flags = panfrost_gem_print_flag("exported", bo->base.base.dma_buf != NULL,
> > +					    has_flags, m);
> > +	if (bo->base.madv < 0)
> > +		has_flags = panfrost_gem_print_flag("purged", true, has_flags, m);
> > +	else if (bo->base.madv > 0)
> > +		has_flags = panfrost_gem_print_flag("purgeable", true, has_flags, m);
> > +	if (!has_flags)
> > +		seq_puts(m, "none");
> > +	seq_puts(m, ")");
> > +
> > +	seq_printf(m, "%-6s0x%-2x", "", bo->debugfs.bo_mask);
> > +
> > +	mutex_lock(&bo->label.lock);
> > +	seq_printf(m, "%-6s%-60s", "", bo->label.str ? : NULL);
> > +	mutex_unlock(&bo->label.lock);
> > +	seq_puts(m, "\n");
> > +
> > +	totals->size += bo->base.base.size;
> > +	totals->resident += resident_size;
> > +	if (bo->base.madv > 0)
> > +		totals->reclaimable += resident_size;
> > +}
> > +
> > +void panthor_gem_debugfs_print_bos(struct panthor_device *ptdev,
> > +				   struct seq_file *m)
> > +{
> > +	struct gem_size_totals totals = {0};
> > +	struct panthor_gem_object *bo;
> > +
> > +	seq_puts(m, "created-by                      global-name     refcount        size            resident-size   file-offset     flags     kflags     label\n");
> > +	seq_puts(m, "------------------------------------------------------------------------------------------------------------------------------------------------\n");
> > +
> > +	scoped_guard(mutex, &ptdev->gems.lock) {
> > +		list_for_each_entry(bo, &ptdev->gems.node, debugfs.node)
> > +			panthor_gem_debugfs_bo_print(bo, m, &totals);
> > +	}
> > +
> > +	seq_puts(m, "==========================================================================================================================================================\n");
> > +	seq_printf(m, "Total size: %zd, Total resident: %zd, Total reclaimable: %zd\n",
> > +		   totals.size, totals.resident, totals.reclaimable);
> > +}
> > +#endif
> > diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> > index 49daa5088a0d..22ecc0d39d5e 100644
> > --- a/drivers/gpu/drm/panthor/panthor_gem.h
> > +++ b/drivers/gpu/drm/panthor/panthor_gem.h
> > @@ -15,6 +15,32 @@ struct panthor_vm;
> >
> >  #define PANTHOR_BO_LABEL_MAXLEN	PAGE_SIZE
> >
> > +#define PANTHOR_BO_KERNEL	BIT(0)
> > +#define PANTHOR_BO_FW_MAPPED	BIT(1)
> > +
> > +/**
> > + * struct panthor_gem_debugfs - GEM object's DebugFS list information
> > + */
> > +struct panthor_gem_debugfs {
> > +	/**
> > +	 * @node: Node used to insert the object in the device-wide list of
> > +	 * GEM objects, to display information about it through a DebugFS file.
> > +	 */
> > +	struct list_head node;
> > +
> > +	/** @creator: Information about the UM process which created the GEM. */
> > +	struct {
> > +		/** @creator.process_name: Group leader name in owning thread's process */
> > +		char process_name[TASK_COMM_LEN];
> > +
> > +		/** @creator.tgid: PID of the thread's group leader within its process */
> > +		pid_t tgid;
> > +	} creator;
> > +
> > +	/** @bo_mask: Bitmask encoding BO type as {USER, KERNEL} x {GPU, FW} */
> > +	u32 bo_mask;
> > +};
> > +
> >  /**
> >   * struct panthor_gem_object - Driver specific GEM object.
> >   */
> > @@ -62,6 +88,10 @@ struct panthor_gem_object {
> >  		/** @lock.str: Protects access to the @label.str field. */
> >  		struct mutex lock;
> >  	} label;
> > +
> > +#ifdef CONFIG_DEBUG_FS
> > +	struct panthor_gem_debugfs debugfs;
> > +#endif
> >  };
> >
> >  /**
> > @@ -157,4 +187,9 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
> >
> >  void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo);
> >
> > +#ifdef CONFIG_DEBUG_FS
> > +void panthor_gem_debugfs_print_bos(struct panthor_device *pfdev,
> > +				   struct seq_file *m);
> > +#endif
> > +
> >  #endif /* __PANTHOR_GEM_H__ */


Adrian Larumbe

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