On Tue, Jul 19 2016 at 6:57pm -0400, Bart Van Assche <bart.vanassche@xxxxxxxxxxx> wrote: > Hello Mike, > > If I run a fio data integrity test against kernel v4.7-rc7 then I > see often that fio reports I/O errors if a path is removed despite > queue_if_no_path having been set in /etc/multipath.conf. Further > analysis showed that this happens because during SCSI device removal > a SCSI device enters state SDEV_CANCEL before the block layer queue > is marked as "dying". In that state I/O requests submitted to that > SCSI device are failed with -EIO. The behavior for > end_clone_request() in drivers/md/dm.c for such requests is as > follows: > - With multiqueue support disabled, call __blk_put_request() and ignore > the "error" argument passed to end_clone_request(). The __blk_put_request() isn't contributing to this blk-mq problem. The need for it is unique to the request_fn case. > - With multiqueue support enabled, pass the "error" argument to > dm_complete_request(). The error arg is passed to dm_complete_request() regardless of queue type but it is only immediately used by the blk-mq API (via blk_mq_complete_request). > Shouldn't end_clone_request() requeue failed requests in both cases > instead of passing the I/O error to the submitter only if multiqueue > is enabled? Pretty sure you'll find it is _not_ blk-mq that is passing the error up. (But if I'm proven wrong that will be welcomed news). The error passed to dm_complete_request() is always used to set tio->error which is later used by dm_done(). DM core handles errors later via softirq in dm_done() -- where the error is passed into the target_type's rq_end_io hook. So in DM multipath you'll see do_end_io() we do finally act on the error we got from the lower layer. And if the error is -EIO, noretry_error() will return true and -EIO will be returned up the IO stack. In the end we're relying on SCSI to properly categorize the underlying faults as retryable vs not -- via SCSI's differentiated IO errors. Unfortunately I'm not seeing anything that DM multipath can do differently here. -EIO is _always_ propagated up. It is strange that all the dm-mq testing that has been done didn't ever catch this. The mptest testsuite is a baseline for validating DM multipath (and request-based DM core) changes. But I've also had Red Hat's QE hammer dm-mq with heavy IO (in terms of the "dt" utility) on a larger NetApp testbed in the face of regular controller faults. Must be this scenario of SDEV_CANCEL is a race that is relatively unique/rare to your testbed? This raises the question: should SCSI be returning something other than -EIO for this case? E.g. an error that is retryable? Mike -- To unsubscribe from this list: 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
