From: Ben Widawsky <benjamin.widaw...@intel.com>
As what was correctly debugged here:
commit acc240d41ea1ab9c488a79219fb313b5b46265ae
Author: Daniel Vetter <daniel.vet...@ffwll.ch>
Date: Thu Dec 5 15:42:34 2013 +0100
drm/i915: Fix use-after-free in do_switch
It then becomes apparent that the default context cannot be the context
being switched to for context switch because it is always bound. It
follows that if the ring->last_context (from) has changed after the
bind_to_gtt, it will always be the default context - this is commented
in the code block.
This assertion will help catch issues without our logic sooner than
letting the system move long (which is possible for some time).
I really want this to be a BUG(), but I also want the patch to get
merged. I think the fact that none of the ERRNOs make any sense at all
is just more evidence that this shouldn't be a WARN.
//Cc: Ian Lister (don't have current email address)
Cc: Rafael Barbalho <rafael.barba...@intel.com>
Signed-off-by: Ben Widawsky <b...@bwidawsk.net>
---
drivers/gpu/drm/i915/i915_gem_context.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c
b/drivers/gpu/drm/i915/i915_gem_context.c
index cfec178..fab74d3 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -690,6 +690,15 @@ static int do_switch_rcs(struct intel_engine_cs *ring,
*/
from = ring->last_context;
+ /* The only context which 'from' can be, if it was changed, is the
default
+ * context. The default context cannot end up in evict everything (as
+ * commented above) because it is always pinned.
+ */
+ if (WARN_ON(from == to)) {
+ ret = -EPERM;
+ goto unpin_out;
+ }
+
if (needs_pd_load) {
/* Older GENs still want the load first, "PP_DCLV followed by
* PP_DIR_BASE register through Load Register Immediate commands
--
1.9.0
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