Hi Jens, while hunting yet another queue stall I've been looking at __blk_mq_tag_busy(): bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx) { if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) && !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state)) atomic_inc(&hctx->tags->active_queues); return true; } Is this some subtle usage of bitops (and I just didn't grasp it) or is the first test_bit() pointless? If the former I _really_ would like to have some comments on why this is required. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html