On 06/11/2013 08:57 PM, James Bottomley wrote: > On Mon, 2013-06-10 at 01:20 -0700, Christoph Hellwig wrote: >> On Mon, Jun 10, 2013 at 09:40:52AM +0200, Hannes Reinecke wrote: >>> When a command runs into a timeout we need to send an 'ABORT TASK' >>> TMF. This is typically done by the 'eh_abort_handler' LLDD callback. >>> >>> Conceptually, however, this function is a normal SCSI command, so >>> there is no need to enter the error handler. >>> >>> This patch implements a new scsi_abort_command() function which >>> invokes an asynchronous function scsi_eh_abort_handler() to >>> abort the commands via 'eh_abort_handler'. >>> >>> If the 'eh_abort_handler' returns SUCCESS or FAST_IO_FAIL the >>> command will be retried if possible. If no retries are allowed >>> the command will be returned immediately, as we have to assume >>> the TMF succeeded and the command is completed with the LLDD. >>> If the TMF fails the command will be pushed back onto the >>> list of failed commands and the SCSI EH handler will be >>> called immediately for all timed-out commands. >> >> Why can't we use a work item per command? Linking things into a list >> just to queue it up to workqueues missed half of the point of the >> workqueue infrastructure. > > Actually, I think we can dump the workqueue altogether. The only reason > we need it is because the current abort handlers wait for the command > and return the completion state. However, all LLDs are capable of > emitting TMFs at interrupt level, so if we separated the emit from the > wait, we could simply do this sequence: > > on timeout, fire the abort from interrupt and mark the command as having > an abort issued (possibly by adding a pointer to the abort task), return > BLK_EH_RESET_TIMER. > > Now if the timeout fires again, assume the abort was unsucessful and > escalate to LUN reset. > > This is fully asynchronous, fully tracked and doesn't rely on work > queues. > Hehe. Been there, done that, doesn't work :-( That was my original idea, too. But some LLDDs send TMFs in a non-interrupt-safe way, so the only way to make it work was to use a workqueue. (Eg qla2xxx has a parameter to send TMFs async, but this doesn't work on older firmware). > The necessary additions for something like this are the from interrupt > issue abort and LUN reset, which could just be additional callbacks in > the host template. > However, we could make that optional, so that LLDDs not capable of sending TMFs in an interrupt-safe manner will continue to use the original framework. Ok, let's see whether this flies. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- 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
