Re: [Intel-gfx] [RFC 5/8] drm/i915: Contexts can use struct pid stored in the client

Chris Wilson
2020-01-10T13:42:23Z

Quoting Tvrtko Ursulin (2020-01-10 13:30:46)
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> Now that contexts keep their parent client reference counted, we can
> remove separate struct pid reference owned by contexts in favour of the
> one already held by the client.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
> drivers/gpu/drm/i915/gem/i915_gem_context.c | 13 ++++---------
> drivers/gpu/drm/i915/gem/i915_gem_context_types.h | 10 ----------
> drivers/gpu/drm/i915/i915_debugfs.c | 7 ++++---
> drivers/gpu/drm/i915/i915_gpu_error.c | 8 ++++----
> 4 files changed, 12 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index ba8ccc754f20..758cebb99ba4 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -323,7 +323,6 @@ static void i915_gem_context_free(struct i915_gem_context *ctx)
> if (ctx->timeline)
> intel_timeline_put(ctx->timeline);
>
> - put_pid(ctx->pid);
> mutex_destroy(&ctx->mutex);
>
> kfree_rcu(ctx, rcu);
> @@ -794,24 +793,20 @@ static int gem_context_register(struct i915_gem_context *ctx,
> WRITE_ONCE(vm->file, fpriv); /* XXX */
> mutex_unlock(&ctx->mutex);
>
> - ctx->pid = get_task_pid(current, PIDTYPE_PID);
> snprintf(ctx->name, sizeof(ctx->name), "%s[%d]",
> - current->comm, pid_nr(ctx->pid));
> + current->comm, pid_nr(client->pid));
>
> /* And finally expose ourselves to userspace via the idr */
> ret = xa_alloc(&fpriv->context_xa, id, ctx, xa_limit_32b, GFP_KERNEL);
> - if (ret) {
> - put_pid(fetch_and_zero(&ctx->pid));
> - goto out;
> - }
> + if (ret)
> + return ret;
>
> ctx->client = client = i915_drm_client_get(fpriv->client);
> spin_lock(&client->ctx_lock);
> list_add_tail_rcu(&ctx->client_link, &client->ctx_list);
> spin_unlock(&client->ctx_lock);
>
> -out:
> - return ret;
> + return 0;
> }
>
> int i915_gem_context_open(struct drm_i915_private *i915,
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
> index 879824159646..23421377a43d 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
> @@ -90,16 +90,6 @@ struct i915_gem_context {
> */
> struct i915_address_space __rcu *vm;
>
> - /**
> - * @pid: process id of creator
> - *
> - * Note that who created the context may not be the principle user,
> - * as the context may be shared across a local socket. However,
> - * that should only affect the default context, all contexts created
> - * explicitly by the client are expected to be isolated.
> - */
> - struct pid *pid;
> -
> /** link: place with &drm_i915_private.context_list */
> struct list_head link;
> struct llist_node free_link;
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 8f01c2bc7355..bc533501b4e0 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -346,7 +346,8 @@ static void print_context_stats(struct seq_file *m,
> rcu_read_unlock();
>
> rcu_read_lock();
> - task = pid_task(ctx->pid ?: file->pid, PIDTYPE_PID);
> + task = pid_task(ctx->client->pid ?: file->pid,
> + PIDTYPE_PID);
> snprintf(name, sizeof(name), "%s",
> task ? task->comm : "<unknown>");
> rcu_read_unlock();
> @@ -1492,10 +1493,10 @@ static int i915_context_status(struct seq_file *m, void *unused)
> spin_unlock(&i915->gem.contexts.lock);
>
> seq_puts(m, "HW context ");
> - if (ctx->pid) {
> + if (ctx->client->pid) {
> struct task_struct *task;
>
> - task = get_pid_task(ctx->pid, PIDTYPE_PID);
> + task = get_pid_task(ctx->client->pid, PIDTYPE_PID);
> if (task) {
> seq_printf(m, "(%s [%d]) ",
> task->comm, task->pid);
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index fda0977d2059..9240327bdb7d 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -1235,8 +1235,8 @@ static void record_request(const struct i915_request *request,
> erq->pid = 0;
> rcu_read_lock();
> ctx = rcu_dereference(request->context->gem_context);
> - if (ctx)
> - erq->pid = pid_nr(ctx->pid);
> + if (ctx && ctx->client->pid)
> + erq->pid = pid_nr(ctx->client->pid);
> rcu_read_unlock();
> }
>
> @@ -1313,11 +1313,11 @@ static bool record_context(struct drm_i915_error_context *e,
> if (ctx && !kref_get_unless_zero(&ctx->ref))
> ctx = NULL;
> rcu_read_unlock();
> - if (!ctx)
> + if (!ctx || !ctx->client->pid)
> return false;

Can we have a client without a pid?

Holding a reference to the ctx is sufficent to protect the
i915_drm_client, ok.

> rcu_read_lock();
> - task = pid_task(ctx->pid, PIDTYPE_PID);
> + task = pid_task(ctx->client->pid, PIDTYPE_PID);
> if (task) {
> strcpy(e->comm, task->comm);
> e->pid = task->pid;

Ok, if you move this ahead to patch 3, we can use this as justification
for i915_drm_client all by itself.
-Chris