[Intel-gfx] [PATCH v4 5/5] drm/i915/gt: Make sure that errors are propagated through request chains

[Rodrigo Vivi]

On Tue, Apr 11, 2023 at 08:39:00AM +0200, Das, Nirmoy wrote:
> 
> On 3/8/2023 10:41 AM, Andi Shyti wrote:
> > Currently, when we perform operations such as clearing or copying
> > large blocks of memory, we generate multiple requests that are
> > executed in a chain.
> > 
> > However, if one of these requests fails, we may not realize it
> > unless it happens to be the last request in the chain. This is
> > because errors are not properly propagated.
> > 
> > For this we need to keep propagating the chain of fence
> > notification in order to always reach the final fence associated
> > to the final request.
> > 
> > To address this issue, we need to ensure that the chain of fence
> > notifications is always propagated so that we can reach the final
> > fence associated with the last request. By doing so, we will be
> > able to detect any memory operation  failures and determine
> > whether the memory is still invalid.
> > 
> > On copy and clear migration signal fences upon completion.
> > 
> > On copy and clear migration, signal fences upon request
> > completion to ensure that we have a reliable perpetuation of the
> > operation outcome.
> > 
> > Fixes: cf586021642d80 ("drm/i915/gt: Pipelined page migration")
> > Reported-by: Matthew Auld <matthew.auld at intel.com>
> > Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
> > Cc: stable at vger.kernel.org
> > Reviewed-by: Matthew Auld <matthew.auld at intel.com>
> With  Matt's comment regarding missing lock in intel_context_migrate_clear
> addressed, this is:
> 
> Acked-by: Nirmoy Das <nirmoy.das at intel.com>

Nack!

Please get some ack from Joonas or Tvrtko before merging this series.

It is a big series targeting stable o.O where the revisions in the cover
letter are not helping me to be confident that this is the right approach
instead of simply reverting the original offending commit:

cf586021642d ("drm/i915/gt: Pipelined page migration")

It looks to me that we are adding magic on top of magic to workaround
the deadlocks, but then adding more waits inside locks... And this with
the hang checks vs heartbeats, is this really an issue on current upstream
code? or was only on DII?

Where was the bug report to start with?

> 
> > ---
> >   drivers/gpu/drm/i915/gt/intel_migrate.c | 41 ++++++++++++++++++-------
> >   1 file changed, 30 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_migrate.c b/drivers/gpu/drm/i915/gt/intel_migrate.c
> > index 3f638f1987968..0031e7b1b4704 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_migrate.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_migrate.c
> > @@ -742,13 +742,19 @@ intel_context_migrate_copy(struct intel_context *ce,
> >   			dst_offset = 2 * CHUNK_SZ;
> >   	}
> > +	/*
> > +	 * While building the chain of requests, we need to ensure
> > +	 * that no one can sneak into the timeline unnoticed.
> > +	 */
> > +	mutex_lock(&ce->timeline->mutex);
> > +
> >   	do {
> >   		int len;
> > -		rq = i915_request_create(ce);
> > +		rq = i915_request_create_locked(ce);
> >   		if (IS_ERR(rq)) {
> >   			err = PTR_ERR(rq);
> > -			goto out_ce;
> > +			break;
> >   		}
> >   		if (deps) {
> > @@ -878,10 +884,14 @@ intel_context_migrate_copy(struct intel_context *ce,
> >   		/* Arbitration is re-enabled between requests. */
> >   out_rq:
> > -		if (*out)
> > +		i915_sw_fence_await(&rq->submit);
> > +		i915_request_get(rq);
> > +		i915_request_add_locked(rq);
> > +		if (*out) {
> > +			i915_sw_fence_complete(&(*out)->submit);
> >   			i915_request_put(*out);
> > -		*out = i915_request_get(rq);
> > -		i915_request_add(rq);
> > +		}
> > +		*out = rq;
> >   		if (err)
> >   			break;
> > @@ -905,7 +915,10 @@ intel_context_migrate_copy(struct intel_context *ce,
> >   		cond_resched();
> >   	} while (1);
> > -out_ce:
> > +	mutex_unlock(&ce->timeline->mutex);
> > +
> > +	if (*out)
> > +		i915_sw_fence_complete(&(*out)->submit);
> >   	return err;
> >   }
> > @@ -1005,7 +1018,7 @@ intel_context_migrate_clear(struct intel_context *ce,
> >   		rq = i915_request_create(ce);
> >   		if (IS_ERR(rq)) {
> >   			err = PTR_ERR(rq);
> > -			goto out_ce;
> > +			break;
> >   		}
> >   		if (deps) {
> > @@ -1056,17 +1069,23 @@ intel_context_migrate_clear(struct intel_context *ce,
> >   		/* Arbitration is re-enabled between requests. */
> >   out_rq:
> > -		if (*out)
> > -			i915_request_put(*out);
> > -		*out = i915_request_get(rq);
> > +		i915_sw_fence_await(&rq->submit);
> > +		i915_request_get(rq);
> >   		i915_request_add(rq);
> > +		if (*out) {
> > +			i915_sw_fence_complete(&(*out)->submit);
> > +			i915_request_put(*out);
> > +		}
> > +		*out = rq;
> > +
> >   		if (err || !it.sg || !sg_dma_len(it.sg))
> >   			break;
> >   		cond_resched();
> >   	} while (1);
> > -out_ce:
> > +	if (*out)
> > +		i915_sw_fence_complete(&(*out)->submit);
> >   	return err;
> >   }