On 07/29/2017 04:42 AM, Paolo Valente wrote: > Groups of BFQ queues are represented by generic entities in BFQ. When > a queue belonging to a parent entity is deactivated, the parent entity > may need to be deactivated too, in case the deactivated queue was the > only active queue for the parent entity. This deactivation may need to > be propagated upwards if the entity belongs, in its turn, to a further > higher-level entity, and so on. In particular, the upward propagation > of deactivation stops at the first parent entity that remains active > even if one of its child entities has been deactivated. > > To decide whether the last non-deactivation condition holds for a > parent entity, BFQ checks whether the field next_in_service is still > not NULL for the parent entity, after the deactivation of one of its > child entity. If it is not NULL, then there are certainly other active > entities in the parent entity, and deactivations can stop. > > Unfortunately, this check misses a corner case: if in_service_entity > is not NULL, then next_in_service may happen to be NULL, although the > parent entity is evidently active. This happens if: 1) the entity > pointed by in_service_entity is the only active entity in the parent > entity, and 2) according to the definition of next_in_service, the > in_service_entity cannot be considered as next_in_service. See the > comments on the definition of next_in_service for details on this > second point. > > Hitting the above corner case causes crashes. > > To address this issue, this commit: > 1) Extends the above check on only next_in_service to controlling both > next_in_service and in_service_entity (if any of them is not NULL, > then no further deactivation is performed) > 2) Improves the (important) comments on how next_in_service is defined > and updated; in particular it fixes a few rather obscure paragraphs Applied, thanks. -- Jens Axboe
