Re: [Intel-gfx] [PATCH 01/11] drm/i915: Release i915_gem_context from a worker

On 13/08/2021 21:30, Daniel Vetter wrote:

The only reason for this really is the i915_gem_engines->fence callback engines_notify(), which exists purely as a fairly funky reference counting scheme for that. Otherwise all other callers are from process context, and generally fairly benign locking context.

There is reset which definitely isn't process context.

Otherwise I did not really get from the commit message is this patch fixing an existing problem or preparing something for the future. If the former then as I wrote above - I am pretty sure there are call sites from the tasklet already.

Regards,

Tvrtko

Unfortunately untangling that requires some major surgery, and we have a few i915_gem_context reference counting bugs that need fixing, and they blow in the current hardirq calling context, so we need a stop-gap measure.

Put a FIXME comment in when this should be removable again.

Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Jon Bloomfield jon.bloomfield@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: "Thomas Hellström" thomas.hellstrom@linux.intel.com Cc: Matthew Auld matthew.auld@intel.com Cc: Lionel Landwerlin lionel.g.landwerlin@intel.com Cc: Dave Airlie airlied@redhat.com Cc: Jason Ekstrand jason@jlekstrand.net

---

drivers/gpu/drm/i915/gem/i915_gem_context.c | 13 +++++++++++-- drivers/gpu/drm/i915/gem/i915_gem_context_types.h | 12 ++++++++++++ 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index fd169cf2f75a..051bc357ff65 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -986,9 +986,10 @@ static struct i915_gem_engines *user_engines(struct i915_gem_context *ctx, return err; }

-void i915_gem_context_release(struct kref *ref) +static void i915_gem_context_release_work(struct work_struct *work) {

• struct i915_gem_context *ctx = container_of(ref, typeof(*ctx), ref);

• struct i915_gem_context *ctx = container_of(work, typeof(*ctx),

• 				    release_work);
  
  

  trace_i915_context_free(ctx); GEM_BUG_ON(!i915_gem_context_is_closed(ctx));

@@ -1002,6 +1003,13 @@ void i915_gem_context_release(struct kref *ref) kfree_rcu(ctx, rcu); }

+void i915_gem_context_release(struct kref *ref) +{

• struct i915_gem_context *ctx = container_of(ref, typeof(*ctx), ref);
• queue_work(ctx->i915->wq, &ctx->release_work);

+}

• static inline struct i915_gem_engines * __context_engines_static(const struct i915_gem_context *ctx) {

@@ -1303,6 +1311,7 @@ i915_gem_create_context(struct drm_i915_private *i915, ctx->sched = pc->sched; mutex_init(&ctx->mutex); INIT_LIST_HEAD(&ctx->link);

• INIT_WORK(&ctx->release_work, i915_gem_context_release_work);

  spin_lock_init(&ctx->stale.lock); INIT_LIST_HEAD(&ctx->stale.engines);

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 94c03a97cb77..0c38789bd4a8 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h @@ -288,6 +288,18 @@ struct i915_gem_context { */ struct kref ref;

• /**

• * @release_work:
  

• *
  

• * Work item for deferred cleanup, since i915_gem_context_put() tends to
  

• * be called from hardirq context.
  

• *
  

• * FIXME: The only real reason for this is &i915_gem_engines.fence, all
  

• * other callers are from process context and need at most some mild
  

• * shuffling to pull the i915_gem_context_put() call out of a spinlock.
  

• */
  

• struct work_struct release_work;
• /**
  • @rcu: rcu_head for deferred freeing.
  */