[PATCH 1/3] drm: add DRM_SET_NAME ioctl
Pierre-Eric Pelloux-Prayer
pierre-eric at damsy.net
Fri Sep 13 12:17:18 UTC 2024
Hi Tvrtko,
Le 12/09/2024 à 10:13, Tvrtko Ursulin a écrit :
>
> On 11/09/2024 15:58, Pierre-Eric Pelloux-Prayer wrote:
>> Giving the opportunity to userspace to associate a free-form
>> name with a drm_file struct is helpful for tracking and debugging.
>>
>> This is similar to the existing DMA_BUF_SET_NAME ioctl.
>>
>> Access to name is protected by a mutex, and the 'clients' debugfs
>> file has been updated to print it.
>>
>> Userspace MR to use this ioctl:
>> https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1428
>
> Idea seems useful to me. Various classes of comments/questions below:
>
>> Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
>> ---
>> drivers/gpu/drm/drm_debugfs.c | 12 ++++++++----
>> drivers/gpu/drm/drm_file.c | 5 +++++
>> drivers/gpu/drm/drm_ioctl.c | 28 ++++++++++++++++++++++++++++
>> include/drm/drm_file.h | 9 +++++++++
>> include/uapi/drm/drm.h | 14 ++++++++++++++
>> 5 files changed, 64 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
>> index 6b239a24f1df..b7492225ae88 100644
>> --- a/drivers/gpu/drm/drm_debugfs.c
>> +++ b/drivers/gpu/drm/drm_debugfs.c
>> @@ -78,12 +78,13 @@ static int drm_clients_info(struct seq_file *m, void *data)
>> kuid_t uid;
>> seq_printf(m,
>> - "%20s %5s %3s master a %5s %10s\n",
>> + "%20s %5s %3s master a %5s %10s %20s\n",
>> "command",
>> "tgid",
>> "dev",
>> "uid",
>> - "magic");
>> + "magic",
>> + "name");
>> /* dev->filelist is sorted youngest first, but we want to present
>> * oldest first (i.e. kernel, servers, clients), so walk backwardss.
>> @@ -94,19 +95,22 @@ static int drm_clients_info(struct seq_file *m, void *data)
>> struct task_struct *task;
>> struct pid *pid;
>> + mutex_lock(&priv->name_lock);
>> rcu_read_lock(); /* Locks priv->pid and pid_task()->comm! */
>> pid = rcu_dereference(priv->pid);
>> task = pid_task(pid, PIDTYPE_TGID);
>> uid = task ? __task_cred(task)->euid : GLOBAL_ROOT_UID;
>> - seq_printf(m, "%20s %5d %3d %c %c %5d %10u\n",
>> + seq_printf(m, "%20s %5d %3d %c %c %5d %10u %20s\n",
>> task ? task->comm : "<unknown>",
>> pid_vnr(pid),
>> priv->minor->index,
>> is_current_master ? 'y' : 'n',
>> priv->authenticated ? 'y' : 'n',
>> from_kuid_munged(seq_user_ns(m), uid),
>> - priv->magic);
>> + priv->magic,
>> + priv->name ? priv->name : "");
>> rcu_read_unlock();
>> + mutex_unlock(&priv->name_lock);
>
> FWIW it is possible you could get away without the need for a lock on the read side if you make the
> pointer RCU managed and stick a synchronize_rcu before kfree in the ioctl update path.
>
> Not because this lock would be a contentended one per se, but mostly to avoid complications such as
> amdgpu_debugfs_gem_info_show() where 3/3 has it broken - cannot take the mutex in rcu locked
> section. Just something to consider in case it would end up simpler code.
I don't mind using RCU or a mutex. Christian suggested a mutex, so I used that, but I'm happy to
switch if the RCU approach is preferred.
>
>> }
>> mutex_unlock(&dev->filelist_mutex);
>> return 0;
>> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
>> index 01fde94fe2a9..558151c3912e 100644
>> --- a/drivers/gpu/drm/drm_file.c
>> +++ b/drivers/gpu/drm/drm_file.c
>> @@ -158,6 +158,7 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor)
>> spin_lock_init(&file->master_lookup_lock);
>> mutex_init(&file->event_read_lock);
>> + mutex_init(&file->name_lock);
>> if (drm_core_check_feature(dev, DRIVER_GEM))
>> drm_gem_open(dev, file);
>> @@ -259,6 +260,10 @@ void drm_file_free(struct drm_file *file)
>> WARN_ON(!list_empty(&file->event_list));
>> put_pid(rcu_access_pointer(file->pid));
>> +
>> + mutex_destroy(&file->name_lock);
>> + kvfree(file->name);
>
> I think kfree is correct here.
>
OK, I'll update in v2.
>> +
>> kfree(file);
>> }
>> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
>> index 51f39912866f..ba2f2120e99b 100644
>> --- a/drivers/gpu/drm/drm_ioctl.c
>> +++ b/drivers/gpu/drm/drm_ioctl.c
>> @@ -540,6 +540,32 @@ int drm_version(struct drm_device *dev, void *data,
>> return err;
>> }
>> +static int drm_set_name(struct drm_device *dev, void *data,
>> + struct drm_file *file_priv)
>> +{
>> + struct drm_set_name *name = data;
>> + void *user_ptr;
>> + char *new_name;
>> +
>> + if (name->name_len >= NAME_MAX)
>> + return -EINVAL;
>
> Any special reason to use the filesystem NAME_MAX?
Not really - feel free to suggest something else.
>
>> +
>> + user_ptr = u64_to_user_ptr(name->name);
>> +
>> + new_name = memdup_user_nul(user_ptr, name->name_len);
>> +
>> + if (IS_ERR(new_name))
>> + return PTR_ERR(new_name);
>> +
>> + mutex_lock(&file_priv->name_lock);
>> + if (file_priv->name)
>> + kvfree(file_priv->name);
>> + file_priv->name = new_name;
>> + mutex_unlock(&file_priv->name_lock);
>
> One question is whether allowing name changes is interesting or it should be one shot?
dma_buf_set_name allows to override the name, so I re-used the same logic.
>
> Second issue is to avoid any Little Bobby Tables situations and somewhat validate the input. At
> least when kernel dumps in in debugfs and fdinfo, we probably don't want to allow userspace to be
> too creative. Like output newlines or some other special characters.
You mean checking "isgraph(c)" for each char? Or even stricter "isalnum(c) || c == '_' || c == '-'"?
Thanks,
Pierre-Eric
>
> Regards,
>
> Tvrtko
>
>> +
>> + return 0;
>> +}
>> +
>> static int drm_ioctl_permit(u32 flags, struct drm_file *file_priv)
>> {
>> /* ROOT_ONLY is only for CAP_SYS_ADMIN */
>> @@ -610,6 +636,8 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
>> DRM_IOCTL_DEF(DRM_IOCTL_PRIME_HANDLE_TO_FD, drm_prime_handle_to_fd_ioctl, DRM_RENDER_ALLOW),
>> DRM_IOCTL_DEF(DRM_IOCTL_PRIME_FD_TO_HANDLE, drm_prime_fd_to_handle_ioctl, DRM_RENDER_ALLOW),
>> + DRM_IOCTL_DEF(DRM_IOCTL_SET_NAME, drm_set_name, DRM_RENDER_ALLOW),
>> +
>> DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETPLANERESOURCES, drm_mode_getplane_res, 0),
>> DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETCRTC, drm_mode_getcrtc, 0),
>> DRM_IOCTL_DEF(DRM_IOCTL_MODE_SETCRTC, drm_mode_setcrtc, DRM_MASTER),
>> diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
>> index 8c0030c77308..df26eee8f79c 100644
>> --- a/include/drm/drm_file.h
>> +++ b/include/drm/drm_file.h
>> @@ -388,6 +388,15 @@ struct drm_file {
>> * Per-file buffer caches used by the PRIME buffer sharing code.
>> */
>> struct drm_prime_file_private prime;
>> +
>> + /**
>> + * @name:
>> + *
>> + * Userspace-provided name; useful for accounting and debugging.
>> + */
>> + const char *name;
>> + /** @name_lock: Protects @name. */
>> + struct mutex name_lock;
>> };
>> /**
>> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
>> index 16122819edfe..fc62bb21f79e 100644
>> --- a/include/uapi/drm/drm.h
>> +++ b/include/uapi/drm/drm.h
>> @@ -1024,6 +1024,12 @@ struct drm_crtc_queue_sequence {
>> __u64 user_data; /* user data passed to event */
>> };
>> +struct drm_set_name {
>> + __u64 name_len;
>> + __u64 name;
>> +};
>> +
>> +
>> #if defined(__cplusplus)
>> }
>> #endif
>> @@ -1288,6 +1294,14 @@ extern "C" {
>> */
>> #define DRM_IOCTL_MODE_CLOSEFB DRM_IOWR(0xD0, struct drm_mode_closefb)
>> +/**
>> + * DRM_IOCTL_SET_NAME - Attach a name to a drm_file
>> + *
>> + * This ioctl is similar to DMA_BUF_SET_NAME - it allows for easier tracking
>> + * and debugging.
>> + */
>> +#define DRM_IOCTL_SET_NAME DRM_IOWR(0xD1, struct drm_set_name)
>> +
>> /*
>> * Device specific ioctls should only be in their respective headers
>> * The device specific ioctl range is from 0x40 to 0x9f.
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