Hi, In Linux 3.14+, SCSI timeouts are handled first without invoking EH; this behavior is on by default but can be disabled with the per-shost-template no_async_abort flag. When a SCSI target is attached to a virtio-scsi HBA and is under I/O stress (lots of concurrent I/O + some I/O running slowly), we see Linux issue commands with duplicate tags, sometimes with tags matching commands which are in the process of being aborted; we see this readily in the Google Compute Engine hypervisor. This behaviour is not seen on Linux <= 3.13 and is not seen if 3.14's virtio_scsi driver has no_async_abort set to 1. An ordering we have seen, from the device perspective: t0: I/O with tag 18446612135224154432 issued t1: TMF Abort for tag 18446612135224154432 t2: Another I/O with the same tag, 18446612135224154432, issued; same offset/size as at t0 [neither the t0 I/O nor the TMF ABORT have yet returned!] Another ordering we have seen, from the device perspective: t0: I/O with tag 18446612135454768576 issued t1: TMF ABORT for tag 18446612135454768576 t2: I/O 18446612135454768576 completes with appropriate cancelled status t3: TMF ABORT completes with OK status t4: New I/O with tag 18446612135454768576, matching size/offset as t0 t5...: [Some other I/Os issued to the same SCSI target] t6...: [TMF ABORT for one of the new I/Os; proper return sequence] t7...: New I/O with tag 18446612135454768576. [Tag 18446612135454768576 has neither completed nor has it been aborted by Linux.] CC-ing stable as 3.14 and 3.15 are affected; a conservative fix is to enable no_async_abort until the problem is better-understood. Thanks, -- vs; -- 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
