From: John Harrison John.C.Harrison@Intel.com
When i915 receives a context reset notification from GuC, it triggers an error capture before resetting any outstanding requsts of that context. Unfortunately, the error capture is not a time bound operation. In certain situations it can take a long time, particularly when multiple large LMEM buffers must be read back and eoncoded. If this delay is longer than other timeouts (heartbeat, test recovery, etc.) then a full GT reset can be triggered in the middle.
That can result in the context being reset by GuC actually being destroyed before the error capture completes and the GuC submission code resumes. Thus, the GuC side can start dereferencing stale pointers and Bad Things ensue.
So add a refcount get of the context during the entire reset operation. That way, the context can't be destroyed part way through no matter what other resets or user interactions occur.
v2: (Matthew Brost) - Update patch to work with async error capture v3: (Matthew Brost) - Drop async capture support as that hasn't landed yet
Signed-off-by: John Harrison John.C.Harrison@Intel.com Signed-off-by: Matthew Brost matthew.brost@intel.com Reviewed-by: Matthew Brost matthew.brost@intel.com --- drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c index 5cc49c0b3889..d7e49f7c1dba 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c @@ -3972,6 +3972,7 @@ int intel_guc_context_reset_process_msg(struct intel_guc *guc, const u32 *msg, u32 len) { struct intel_context *ce; + unsigned long flags; int desc_idx;
if (unlikely(len != 1)) { @@ -3980,11 +3981,24 @@ int intel_guc_context_reset_process_msg(struct intel_guc *guc, }
desc_idx = msg[0]; + + /* + * The context lookup uses the xarray but lookups only require an RCU lock + * not the full spinlock. So take the lock explicitly and keep it until the + * context has been reference count locked to ensure it can't be destroyed + * asynchronously until the reset is done. + */ + xa_lock_irqsave(&guc->context_lookup, flags); ce = g2h_context_lookup(guc, desc_idx); + if (ce) + intel_context_get(ce); + xa_unlock_irqrestore(&guc->context_lookup, flags); + if (unlikely(!ce)) return -EPROTO;
guc_handle_context_reset(guc, ce); + intel_context_put(ce);
return 0; }