On Jun 24, 2013, at 9:26 PM, Mike Christie <michaelc@xxxxxxxxxxx> wrote: > On 06/24/2013 05:27 PM, James Bottomley wrote: >>>> However, what's the reasoning behind wanting to do this? In theory all >>>> necessary resources for the eh thread should only be freed in the >>>> release callback. That means they aren't freed until all error recovery >>>> completes. >>> >>> I think it makes it easier to handle cleanup of driver resources >>> needed >>> for aborts/resets for some drivers. If after host removal, the scsi eh >>> can call into the driver after scsi_remove_host is called then we have >>> to set some internal bits to fail future eh callback calls and handle >>> waiting on or flushing running eh operations. If we know that after >>> scsi_host_remove is called the eh callbacks will not be running and >>> will >>> not be called we can just free the driver resources. >>> >>> For iscsi and I think drivers that do scsi_remove_target it would be >>> helpful to have something similar at the target level. >> >> I'm wary of this because it combines two models: a definite state model >> (where we move from state to state waiting for the completions) with an >> event driven one (in theory the current one); such combinations rarely >> lead to good things because you get a mixture of actions causing state >> transitions some of which are waited for and some of which have an async >> transition and that ends up confusing the heck out of everybody no >> matter how carefully documented. Can you give me some use cases of what >> you're trying to achieve? Could it be as simple as an event that fires >> on release? > > > The problem that we hit in iscsi is that we will call scsi_remove_target > (we used to call scsi_remove_host when we always did a host per target > so we hit the problem at that level before). That will complete, but the > scsi eh might still be trying to abort/reset devices accessed through > that target. To avoid freeing resources that the iscsi scsi eh might be > using, we set internal state bits and wait on host_busy to go to zero > before we tear down the iscsi session, conn and task structs. > > I think Bart was hitting a similar issue but a level up in the host > removal case, because srp always does a host per target and so it just > does a scsi_remove_host.. I take this back. I don't think it is a issue anymore and I think I can remove the iscsi hack. With the blk_cleanup_queue/blk_drain_queue code I think the target and the removal of its devices will not complete until the scsi eh is completed. The blk_drain_queue code will now wait for the eh to complete because the rq counters will be incremented.-- 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
