Thank you for your contribution! Sashiko AI review found 2 potential issues to consider: - [Medium] scsi: multipath: premature bio completion in scsi_mpath_end_request() - [Medium] scsi-multipath: mismatched bdev I/O accounting in scsi_mpath_end_request() --
commit 29255340e39c30a34f5cb1da674871fdd2c627ea Author: John Garry <[email protected]> scsi-multipath: add scsi_mpath_{start,end}_request() This commit adds scsi_mpath_start_request() and scsi_mpath_end_request() to track per-host active multipath requests for the queue-depth I/O policy and perform block device I/O accounting on multipath requests. > diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c > index 2f47c39d82936..93a4545f1dbf7 100644 > --- a/drivers/scsi/scsi_multipath.c > +++ b/drivers/scsi/scsi_multipath.c > @@ -545,6 +545,75 @@ void scsi_mpath_put_head(struct scsi_mpath_head > *scsi_mpath_head) > } > EXPORT_SYMBOL_GPL(scsi_mpath_put_head); > > +void scsi_mpath_start_request(struct request *req) > +{ > + struct scsi_cmnd *scmd = blk_mq_rq_to_pdu(req); > + struct scsi_device *sdev = scmd->device; > + struct scsi_mpath_device *scsi_mpath_dev = sdev->scsi_mpath_dev; > + struct scsi_mpath_head *scsi_mpath_head = > + scsi_mpath_dev->scsi_mpath_head; > + struct bio *clone = req->bio, *master; > + struct mpath_head *mpath_head = &scsi_mpath_head->mpath_head; > + struct gendisk *disk = mpath_head->disk; > + > + if (mpath_qd_iopolicy(&scsi_mpath_head->iopolicy) && > + !(scmd->flags & SCMD_MPATH_CNT_ACTIVE)) { > + struct Scsi_Host *shost = sdev->host; > + > + atomic_inc(&shost->mpath_nr_active); > + scmd->flags |= SCMD_MPATH_CNT_ACTIVE; > + } > + > + if (blk_rq_is_passthrough(req) || !blk_queue_io_stat(disk->queue)) > + return; > + > + if (!clone) { > + scmd->flags &= ~SCMD_MPATH_IO_STATS; > + return; > + } > + > + if (scmd->flags & SCMD_MPATH_IO_STATS) > + return; > + > + master = clone->bi_private; > + > + scmd->flags |= SCMD_MPATH_IO_STATS; > + scmd->start_time = bdev_start_io_acct(master->bi_bdev, req_op(req), > + jiffies); > + scmd->start_bytes = blk_rq_bytes(req); > +} > + > +bool scsi_mpath_end_request(struct request *req, blk_status_t error, > + unsigned int nr_bytes) > +{ > + struct scsi_cmnd *scmd = blk_mq_rq_to_pdu(req); > + struct scsi_device *sdev = scmd->device; > + struct block_device *bi_bdev = NULL; > + > + if (scmd->flags & SCMD_MPATH_IO_STATS) { > + struct bio *clone = req->bio, *master = clone->bi_private; > + > + bi_bdev = master->bi_bdev; > + } [Severity: Medium] Can scsi_mpath_start_request() and scsi_mpath_end_request() account I/O against different block_device structures when a merged request completes partially? scsi_mpath_clone_bio() directs all clone bios to the underlying path disk's part0 while storing the original bio in clone->bi_private. Contiguous clone bios from adjacent partitions on mpath_head->disk can therefore be merged into a single request on sdev->request_queue. When that request starts, scsi_mpath_start_request() calls bdev_start_io_acct() on the first bio's master->bi_bdev and sets SCMD_MPATH_IO_STATS. If a partial completion advances req->bio past the first bio (returning true from blk_update_request()), the final call to scsi_mpath_end_request() re-derives bi_bdev from the remaining bio's master->bi_bdev and calls bdev_end_io_acct() on the second partition, leaking in_flight on the first partition and underflowing it on the second. Accounting against mpath_head->disk->part0 in both functions (or saving the accounted block_device) would keep the start and end calls paired. > + > + if (blk_update_request(req, error, nr_bytes)) > + return true; > + > + if (scmd->flags & SCMD_MPATH_CNT_ACTIVE) { > + struct Scsi_Host *shost = sdev->host; > + > + atomic_dec_if_positive(&shost->mpath_nr_active); > + } > + > + if (!(scmd->flags & SCMD_MPATH_IO_STATS)) > + return false; > + bdev_end_io_acct(bi_bdev, req_op(req), > + scmd->start_bytes >> SECTOR_SHIFT, > + scmd->start_time); > + > + return false; > +} [Severity: Medium] Does calling blk_update_request() before updating shost->mpath_nr_active and calling bdev_end_io_acct() complete master_bio too early? blk_update_request() runs bio_endio(clone) -> scsi_mpath_clone_end_io(), which either schedules mpath_head->requeue_work on a path error or calls bio_endio(master_bio). Because mpath_head->disk is bio-based, __submit_bio() drops its queue reference as soon as mpath_bdev_submit_bio() returns, so nothing pins bi_bdev once master_bio completes: CPU0 CPU1 scsi_mpath_end_request() blk_update_request() ... scsi_mpath_clone_end_io() bio_endio(master_bio) blkdev_put() bdev_del_partition() ... bdev_free_inode() free_percpu(bdev->bd_stats) bdev_end_io_acct(bi_bdev, ...) <-- use-after-free on bi_bdev In addition, when scsi_mpath_clone_end_io() triggers failover or a caller immediately submits dependent I/O under MPATH_IOPOLICY_QD, mpath_queue_depth_path() reads shost->mpath_nr_active before this request has decremented it. -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=21
