On 02/24/2017 05:01 AM, Bart Van Assche wrote: > On Wed, 2017-02-22 at 17:07 +0100, Hannes Reinecke wrote: >> Primary goal is to make asynchronous aborts mandatory; there hasn't >> been a single report so far where asynchronous abort won't work, so >> the 'no_async_abort' flag has never been used and will be removed >> with this patchset. > > Hello Hannes, > > There is a problem with asynchronous aborts. Some SCSI drivers, e.g. ib_srp, > support fast error recovery by performing a transport layer reconnect without > reporting this event as a failure to the SCSI core. While such a reconnect is > ongoing it is important that no attempt is made to use the data structures > that represent the connection. Hence the scsi_target_block() call in > srp_reconnect_rport(). This blocks most .queuecommand() calls except those > that originate from the SCSI EH. Hence the if (current == shost->ehandler) > mutex_lock(&rport->mutex) code in srp_queuecommand(). Asynchronous aborts > break this code because the asynchronous abort code submits an abort from > another context than the SCSI EH thread. I know that this way of detecting > the SCSI EH context is not an optimal solution. A few years ago I have tried > to modify the SCSI EH such that reconnects and .queuecommand() calls could > be serialized but James was not interested in such patches at that time. > Don't think that's much of an issue. scsi_abort_command() (ie the call which triggers async aborts) is only called if the .eh_timed_out() callback returns BLK_EH_NOT_HANDLED. So during reconnects we will not schedule any calls to async aborts. We _might_ have scheduled an async abort prior to a call to srp_reconnect_rport(), but that would be equivalent with calling srp_reconnect_rport() with commands still in flight. Is that even possible? If so, how do you handle these commands after reconnect returns? Any I_T_L nexus will be gone from the target, right? Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg)
