On Fri, 13 Jul 2012 14:14:05 +0100
Chris Wilson <ch...@chris-wilson.co.uk> wrote:
> Otherwise we end up trying to unpin a freed object and BUG.
>
Just a quick excuse: originally do_switch was just a very low level
helper, and everything called i915_switch_context (including default
setup), so the bug likely didn't exist in older revisions of the series.
Since you're moving around so much code, maybe we could just move
do_switch() a bit higher in the file so we don't have to do the forward
declaration crap anymore?
I am a bit confused why I didn't hit this in my testing, but thanks for
tracking it down. I must say though, really like this patch, and the
cleanups it does in addition to fixing the bug is way understated in the
commit message. Still, a couple of comments below.
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <b...@bwidawsk.net>
> ---
> drivers/gpu/drm/i915/i915_gem_context.c | 82
> +++++++++++--------------------
> 1 file changed, 30 insertions(+), 52 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c
> b/drivers/gpu/drm/i915/i915_gem_context.c
> index 90857f8..b0a855f 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -97,8 +97,7 @@
>
> static struct i915_hw_context *
> i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id);
> -static int do_switch(struct drm_i915_gem_object *from_obj,
> - struct i915_hw_context *to, u32 seqno);
> +static int do_switch(struct i915_hw_context *to);
>
> static int get_context_size(struct drm_device *dev)
> {
> @@ -220,26 +219,24 @@ static int create_default_context(struct
> drm_i915_private *dev_priv)
> */
> dev_priv->ring[RCS].default_context = ctx;
> ret = i915_gem_object_pin(ctx->obj, CONTEXT_ALIGN, false);
> - if (ret) {
> - do_destroy(ctx);
> - return ret;
> - }
> + if (ret)
> + goto err_destroy;
>
> ret = i915_gem_object_set_to_gtt_domain(ctx->obj, true);
> - if (ret) {
> - i915_gem_object_unpin(ctx->obj);
> - do_destroy(ctx);
> - return ret;
> - }
> + if (ret)
> + goto err_unpin;
>
> - ret = do_switch(NULL, ctx, 0);
> - if (ret) {
> - i915_gem_object_unpin(ctx->obj);
> - do_destroy(ctx);
> - } else {
> - DRM_DEBUG_DRIVER("Default HW context loaded\n");
> - }
> + ret = do_switch(ctx);
> + if (ret)
> + goto err_unpin;
>
> + DRM_DEBUG_DRIVER("Default HW context loaded\n");
> + return 0;
> +
> +err_unpin:
> + i915_gem_object_unpin(ctx->obj);
> +err_destroy:
> + do_destroy(ctx);
> return ret;
> }
>
> @@ -366,16 +363,14 @@ mi_set_context(struct intel_ring_buffer *ring,
> return ret;
> }
>
> -static int do_switch(struct drm_i915_gem_object *from_obj,
> - struct i915_hw_context *to,
> - u32 seqno)
> +static int do_switch(struct i915_hw_context *to)
> {
> - struct intel_ring_buffer *ring = NULL;
> + struct drm_i915_gem_object *from_obj = to->ring->last_context_obj;
> u32 hw_flags = 0;
> int ret;
>
> - BUG_ON(to == NULL);
> - BUG_ON(from_obj != NULL && from_obj->pin_count == 0);
> + if (from_obj == to->obj)
> + return 0;
The second BUG_ON I think is still fairly useful (though it would be
nicer to have a context_id in the object so we could check at the time
of unpin).
>
> ret = i915_gem_object_pin(to->obj, CONTEXT_ALIGN, false);
> if (ret)
> @@ -389,8 +384,7 @@ static int do_switch(struct drm_i915_gem_object *from_obj,
> else if (WARN_ON_ONCE(from_obj == to->obj)) /* not yet expected */
> hw_flags |= MI_FORCE_RESTORE;
>
> - ring = to->ring;
> - ret = mi_set_context(ring, to, hw_flags);
> + ret = mi_set_context(to->ring, to, hw_flags);
> if (ret) {
> i915_gem_object_unpin(to->obj);
> return ret;
> @@ -403,6 +397,7 @@ static int do_switch(struct drm_i915_gem_object *from_obj,
> * MI_SET_CONTEXT instead of when the next seqno has completed.
> */
> if (from_obj != NULL) {
> + u32 seqno = i915_gem_next_request_seqno(to->ring);
I haven't really looked hard, but we do end up here quite early in init,
reset, unfreeze. Hopefully this is always safe to do.
> /* As long as MI_SET_CONTEXT is serializing, ie. it flushes the
> * whole damn pipeline, we don't need to explicitly mark the
> * object dirty. The only exception is that the context must be
> @@ -412,13 +407,15 @@ static int do_switch(struct drm_i915_gem_object
> *from_obj,
> */
> from_obj->base.write_domain = I915_GEM_DOMAIN_INSTRUCTION;
> from_obj->base.read_domains = I915_GEM_DOMAIN_INSTRUCTION;
> - i915_gem_object_move_to_active(from_obj, ring, seqno);
> + i915_gem_object_move_to_active(from_obj, to->ring, seqno);
> from_obj->dirty = 1;
> BUG_ON(from_obj->ring != to->ring);
> i915_gem_object_unpin(from_obj);
> + drm_gem_object_unreference(&from_obj->base);
> }
>
> - ring->last_context_obj = to->obj;
> + drm_gem_object_reference(&to->obj->base);
> + to->ring->last_context_obj = to->obj;
> to->is_initialized = true;
>
> return 0;
> @@ -442,10 +439,7 @@ int i915_switch_context(struct intel_ring_buffer *ring,
> int to_id)
> {
> struct drm_i915_private *dev_priv = ring->dev->dev_private;
> - struct drm_i915_file_private *file_priv = NULL;
> struct i915_hw_context *to;
> - struct drm_i915_gem_object *from_obj = ring->last_context_obj;
> - int ret;
>
> if (dev_priv->hw_contexts_disabled)
> return 0;
> @@ -453,34 +447,18 @@ int i915_switch_context(struct intel_ring_buffer *ring,
> if (ring != &dev_priv->ring[RCS])
> return 0;
>
> - if (file)
> - file_priv = file->driver_priv;
> -
> if (to_id == DEFAULT_CONTEXT_ID) {
> to = ring->default_context;
> } else {
> - to = i915_gem_context_get(file_priv, to_id);
> + if (file == NULL)
> + return -EINVAL;
> +
> + to = i915_gem_context_get(file->driver_priv, to_id);
> if (to == NULL)
> return -ENOENT;
> }
>
> - if (from_obj == to->obj)
> - return 0;
> -
> - ret = do_switch(from_obj, to, i915_gem_next_request_seqno(to->ring));
> - if (ret)
> - return ret;
> -
> - /* Just to make the code a little cleaner we take the object reference
> - * after the switch was successful. It would be more intuitive to ref
> - * the 'to' object before the switch but we know the refcount must be >0
> - * if context_get() succeeded, and we hold struct mutex. So it's safe to
> - * do this here/now
> - */
> - drm_gem_object_reference(&to->obj->base);
> - if (from_obj != NULL)
> - drm_gem_object_unreference(&from_obj->base);
> - return ret;
> + return do_switch(to);
> }
>
> int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
--
Ben Widawsky, Intel Open Source Technology Center
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