Hello, James, Jens and Christoph. This patchset is reworked version of the previous REQ_SPECIAL update patchset. Patches #01 and #05 update blk layer. The other patches update SCSI midlayer. I've opted for automatically setting REQ_SOFTBARRIER together with REQ_STARTED in elv_next_request(). Reordering prep-deferred or requeued requests doesn't have any real benefit and actually both as and cfq don't reorder requeued requests. The only behavior change is that prep-deferred requests can't be passed by others. I think the change is a good thing. The only affected driver other than SCSI is i2o_block. So, Jens, please let me know what you think. This patchset does the following things. #01 : make elv_next_request() set REQ_SOFTBARRIER in addition to REQ_STARTED. #02-04 : decouple REQ_SPECIAL from scsi_cmnd->special and make it mean special requests (non-fs/pc). #05 : remove requeue feature from blk_insert_request(). Previously, REQ_SPECIAL duplicately meant the request has been prepp'ed by SCSI midlayer and/or the request is a special request. This left special requests handling in the midlayer subtley inconsistent. Also, the setting of REQ_SPECIAL was done by the block layer using blk_insert_request() mostly but sometimes by the SCSI midlayer (when returning BLK_PREP_DEFER from scsi_prep_fn()). blk_insert_request() was used for two different purposes. * enqueue special requests * turn on REQ_SPECIAL|REQ_SOFTBARRIER and call blk_requeue_request(). The second somewhat unobvious feature of blk_insert_request() is used only by SCSI midlayer and SCSI midlayer depended on it to set REQ_SOFTBARRIER. Unfortunately, when the SCSI midlayer sets REQ_SPECIAL explicitly (sg allocation failure path) it didn't set REQ_SOFTBARRIER, creating a *highly* unlikely but still existing dead lock condition caused by allowing reorder of a request which has its cmd allocated. IMHO, this proves the subtlety of current situation. This patchset makes blk layer set REQ_SOFTBARRIER automatically when a request is dispatched from its request queue and SCSI midlayer use blk_requeue_request() for requeueing. To prevent more misuses, the requeue feature of blk_insert_request() is removed. Requeueing should be done with blk_requeue_request() not blk_insert_request(). [ Start of patch descriptions ] 01_scsi_blk_make_started_requests_ordered.patch : make blk layer set REQ_SOFTBARRIER when a request is dispatched Reordering already started requests is without any real benefit and causes problems if the request has its driver-specific resources allocated (as in SCSI). This patch makes elv_next_request() set REQ_SOFTBARRIER automatically when a request is dispatched. As both as and cfq schedulers don't allow passing requeued requests, the only behavior change is that requests deferred by prep_fn won't be passed by other requests. This change shouldn't cause any problem. The only affected driver other than SCSI is i2o_block. 02_scsi_REQ_SPECIAL_semantic_scsi_init_io.patch : remove REQ_SPECIAL in scsi_init_io() scsi_init_io() used to set REQ_SPECIAL when it fails sg allocation before requeueing the request by returning BLKPREP_DEFER. REQ_SPECIAL is being updated to mean special requests. So, remove REQ_SPECIAL setting. 03_scsi_REQ_SPECIAL_semantic_scsi_queue_insert.patch : make scsi_queue_insert() use blk_requeue_request() scsi_queue_insert() used to use blk_insert_request() for requeueing requests. This depends on the unobvious behavior of blk_insert_request() setting REQ_SPECIAL and REQ_SOFTBARRIER when requeueing. This patch makes scsi_queue_insert() use blk_requeue_request(). As REQ_SPECIAL means special requests and REQ_SOFTBARRIER is automatically handled by blk layer now, no flag needs to be set. Note that scsi_queue_insert() now calls scsi_run_queue() itself, and the prototype of the function is added right above scsi_queue_insert(). This is temporary, as later requeue path consolidation patchset removes scsi_queue_insert(). By adding temporary prototype, we can do away with unnecessarily moving functions. 04_scsi_REQ_SPECIAL_semantic_scsi_requeue_command.patch : make scsi_requeue_request() use blk_requeue_request() scsi_requeue_request() used to use blk_insert_request() for requeueing requests. This depends on the unobvious behavior of blk_insert_request() setting REQ_SPECIAL and REQ_SOFTBARRIER when requeueing. This patch makes scsi_queue_insert() use blk_requeue_request(). As REQ_SPECIAL means special requests and REQ_SOFTBARRIER is automatically handled by blk layer now, no flag needs to be set. 05_scsi_blk_insert_request_no_requeue.patch : remove requeue feature from blk_insert_request() blk_insert_request() has a unobivous feature of requeuing a request setting REQ_SPECIAL|REQ_SOFTBARRIER. SCSI midlayer was the only user and as previous patches removed the usage, remove the feature from blk_insert_request(). Only special requests should be queued with blk_insert_request(). All requeueing should go through blk_requeue_request(). [ End of patch descriptions ] Thanks. - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
