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Message-ID: <e39f64ee-077e-4e0e-87f5-fb03e765380e@arm.com>
Date: Mon, 23 Sep 2024 10:51:47 +0100
From: Steven Price <steven.price@....com>
To: Mary Guillemard <mary.guillemard@...labora.com>,
linux-kernel@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org,
Boris Brezillon <boris.brezillon@...labora.com>,
Christopher Healy <healych@...zon.com>, kernel@...labora.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>, Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 2/2] drm/panthor: Expose scheduler groups info in debugfs
On 18/09/2024 09:50, Mary Guillemard wrote:
> This adds a new debugfs file named "sched_groups" allowing a user to
> query information about all userspace clients scheduler groups.
>
> As we uses drm_device.filelist to achieve it, we also expose the
> client_id with the task information to differentiate one client
> from another inside the same task.
>
> Signed-off-by: Mary Guillemard <mary.guillemard@...labora.com>
Can you explain a bit more why you want this? I'm not against the idea
but I'm wary of adding 'debugging features' because often they fall into
one of two camps:
* Genuinely useful features that shouldn't be in debugfs because people
want a stable API.
* Niche features that take maintainance effort despite not being
particularly useful.
> ---
> drivers/gpu/drm/panthor/panthor_drv.c | 1 +
> drivers/gpu/drm/panthor/panthor_sched.c | 127 ++++++++++++++++++++++++
> drivers/gpu/drm/panthor/panthor_sched.h | 4 +
> 3 files changed, 132 insertions(+)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index 0d825d63d712..aa390597d355 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -1450,6 +1450,7 @@ static const struct file_operations panthor_drm_driver_fops = {
> static void panthor_debugfs_init(struct drm_minor *minor)
> {
> panthor_mmu_debugfs_init(minor);
> + panthor_sched_debugfs_init(minor);
> }
> #endif
>
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index f15abeef4ece..0c1ddbfbe164 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -1,6 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0 or MIT
> /* Copyright 2023 Collabora ltd. */
>
> +#include <drm/drm_debugfs.h>
> #include <drm/drm_drv.h>
> #include <drm/drm_exec.h>
> #include <drm/drm_gem_shmem_helper.h>
> @@ -3581,3 +3582,129 @@ int panthor_sched_init(struct panthor_device *ptdev)
> ptdev->scheduler = sched;
> return 0;
> }
> +
> +#ifdef CONFIG_DEBUG_FS
> +static const char *panthor_csg_priority_names[PANTHOR_CSG_PRIORITY_COUNT] = {
> + "LOW",
> + "MEDIUM",
> + "HIGH",
> + "REALTIME"
> +};
> +
> +static const char *panthor_group_state_names[PANTHOR_CS_GROUP_UNKNOWN_STATE] = {
> + "CREATED",
> + "ACTIVE",
> + "SUSPENDED",
> + "TERMINATED"
> +};
> +
> +static void show_panthor_queue(const struct panthor_queue *queue,
> + u32 queue_index,
> + struct seq_file *m)
> +{
> + seq_printf(m, "queue %u:", queue_index);
> + seq_printf(m, " priority %u", queue->priority);
> + seq_printf(m, " doorbell_id %d", queue->doorbell_id);
> + seq_puts(m, "\n");
> +}
> +
> +static void show_panthor_group(struct panthor_group *group,
> + u32 group_handle,
> + struct seq_file *m)
> +{
> + u32 i;
> +
> + group_get(group);
This looks wrong - this function relies on group not becoming invalid
before the call, so we'd better be holding a sufficient lock/reference
on the group before show_panthor_group() is called otherwise we've got a
race before the group_get() call.
Although I can see this bug is present elsewhere in panthor_sched.c now
I look...
> +
> + seq_printf(m, "group %u:", group_handle);
> + seq_printf(m, " priority %s", group->priority < PANTHOR_CSG_PRIORITY_COUNT ?
> + panthor_csg_priority_names[group->priority] : "UNKNOWN");
> + seq_printf(m, " state %s", group->state < PANTHOR_CS_GROUP_UNKNOWN_STATE ?
> + panthor_group_state_names[group->state] : "UNKNOWN");
> + seq_printf(m, " csg_id %d", group->csg_id);
> + seq_printf(m, " csg_priority %d", group->csg_priority);
> + seq_printf(m, " compute_core_mask 0x%016llx", group->compute_core_mask);
> + seq_printf(m, " fragment_core_mask 0x%016llx", group->fragment_core_mask);
> + seq_printf(m, " tiler_core_mask 0x%016llx", group->tiler_core_mask);
> + seq_printf(m, " max_compute_cores %d", group->max_compute_cores);
> + seq_printf(m, " max_fragment_cores %d", group->max_fragment_cores);
> + seq_printf(m, " max_tiler_cores %d", group->max_tiler_cores);
> + seq_puts(m, "\n");
> +
> + for (i = 0; i < group->queue_count; i++)
> + show_panthor_queue(group->queues[i], i, m);
> +
> + group_put(group);
> +}
> +
> +static int show_file_group_pool(const struct panthor_file *pfile, struct seq_file *m)
> +{
> + struct panthor_group_pool *gpool = pfile->groups;
> + struct panthor_group *group;
> + unsigned long i;
> +
> + if (IS_ERR_OR_NULL(gpool))
> + return 0;
> +
> + xa_for_each(&gpool->xa, i, group)
> + show_panthor_group(group, i, m);
Here I see no protection against a racing call to PANTHOR_GROUP_DESTROY,
so group could become invalid between xa_for_each returning it and the
call to show_panthor_group().
Steve
> +
> + return 0;
> +}
> +
> +static int show_each_file(struct seq_file *m, void *arg)
> +{
> + struct drm_info_node *node = (struct drm_info_node *)m->private;
> + struct drm_device *ddev = node->minor->dev;
> + int (*show)(const struct panthor_file *, struct seq_file *) = node->info_ent->data;
> + struct drm_file *file;
> + int ret;
> +
> + ret = mutex_lock_interruptible(&ddev->filelist_mutex);
> + if (ret)
> + return ret;
> +
> + list_for_each_entry(file, &ddev->filelist, lhead) {
> + struct task_struct *task;
> + struct panthor_file *pfile = file->driver_priv;
> + struct pid *pid;
> +
> + /*
> + * Although we have a valid reference on file->pid, that does
> + * not guarantee that the task_struct who called get_pid() is
> + * still alive (e.g. get_pid(current) => fork() => exit()).
> + * Therefore, we need to protect this ->comm access using RCU.
> + */
> + rcu_read_lock();
> + pid = rcu_dereference(file->pid);
> + task = pid_task(pid, PIDTYPE_TGID);
> + seq_printf(m, "client_id %8llu pid %8d command %s:\n", file->client_id,
> + pid_nr(pid), task ? task->comm : "<unknown>");
> + rcu_read_unlock();
> +
> + ret = show(pfile, m);
> + if (ret < 0)
> + break;
> +
> + seq_puts(m, "\n");
> + }
> +
> + mutex_unlock(&ddev->filelist_mutex);
> + return ret;
> +}
> +
> +static struct drm_info_list panthor_sched_debugfs_list[] = {
> + { "sched_groups", show_each_file, 0, show_file_group_pool },
> +};
> +
> +/**
> + * panthor_sched_debugfs_init() - Initialize scheduler debugfs entries
> + * @minor: Minor.
> + */
> +void panthor_sched_debugfs_init(struct drm_minor *minor)
> +{
> + drm_debugfs_create_files(panthor_sched_debugfs_list,
> + ARRAY_SIZE(panthor_sched_debugfs_list),
> + minor->debugfs_root, minor);
> +}
> +#endif /* CONFIG_DEBUG_FS */
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
> index 3a30d2328b30..577239aa66bf 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.h
> +++ b/drivers/gpu/drm/panthor/panthor_sched.h
> @@ -47,4 +47,8 @@ void panthor_sched_resume(struct panthor_device *ptdev);
> void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
> void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
>
> +#ifdef CONFIG_DEBUG_FS
> +void panthor_sched_debugfs_init(struct drm_minor *minor);
> +#endif
> +
> #endif
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