On Tue, 2010-10-26 at 17:27 -0500, James Bottomley wrote: > On Tue, 2010-10-26 at 15:08 -0700, Nicholas A. Bellinger wrote: > > On Thu, 2010-10-21 at 08:08 -0700, Mike Anderson wrote: > > > Nicholas A. Bellinger <nab@xxxxxxxxxxxxxxx> wrote: > > > > *) core drivers/scsi remaining issue(s): > > > > > > > > The issue raised by andmike during RFCv4 described as: > > > > > > > > "If we skip __scsi_try_to_abort_cmd when REQ_ATOM_COMPLETE is set it > > > > would be correct for the scsi_decide_disposition cases but it would > > > > appear this would stop __scsi_try_to_abort_cmd from being called in the > > > > time out case as REQ_ATOM_COMPLETE is set prior to calling > > > > blk_rq_timed_out." > > > > > > > > The complete discussion is here: > > > > > > > > http://marc.info/?l=linux-scsi&m=128535319915212&w=2 > > > > > > > > We still need folks with experience to dig into this code, so you know > > > > the scsi_error.c code please jump in! > > > > > > > > > > I provided two logging traces below for the two cases mentioned in the > > > above email thread. The second trace used a modified version of > > > scsi_debug so that I could generate the needed unit attention codes. > > > 1.) On the check for complete comment the logging below marked with > > > "***" indicated that during a timeout that the complete bit is set. We > > > would not want to have a check for complete skip the call to > > > __scsi_try_to_abort_cmd. > > > > > > scsi_debug: cmd 28 00 00 00 00 00 00 00 20 00 > > > sd 1:0:0:0: [sdb] Done: TIMEOUT > > > sd 1:0:0:0: [sdb] Result: hostbyte=DID_OK driverbyte=DRIVER_OK > > > sd 1:0:0:0: [sdb] CDB: Read(10): 28 00 00 00 00 00 00 00 20 00 > > > Waking error handler thread > > > Error handler scsi_eh_1 waking up > > > sd 1:0:0:0: scsi_eh_prt_fail_stats: cmds failed: 0, cancel: 1 > > > Total of 1 commands on 1 devices require eh work > > > scsi_eh_1: aborting cmd:0xffff88019e171b80 > > > > > > *** > > > sd 1:0:0:0: scsi_try_to_abort_cmd: Comp bit set > > > *** > > > > > > scsi_debug: abort > > > scsi_debug: cmd 00 00 00 00 00 00 > > > scsi_eh_done scmd: ffff88019e171b80 result: 0 > > > scsi_send_eh_cmnd: scmd: ffff88019e171b80, timeleft: 10000 > > > scsi_send_eh_cmnd: scsi_eh_completed_normally 2002 > > > scsi_eh_tur: scmd ffff88019e171b80 rtn 2002 > > > scsi_eh_1: flush retry cmd: ffff88019e171b80 > > > scsi_restart_operations: waking up host to restart > > > scsi_debug: cmd 28 00 00 00 00 00 00 00 20 00 > > > Error handler scsi_eh_1 sleeping > > > > > > > Hi Mike and Co, > > > > After considering a couple of different approches here, I ended up with > > the following simple patch that has been tested on linus HEAD from this > > afternoon w/ forcing scsi_debug cmd TIMEOUT during modprobe and via > > sg_dd ops. (See comments below) > > > > [PATCH] scsi: Add SCSI_EH_SOFTIRQ_DONE usage > > > > This patch introduces a SCSI_EH_SOFTIRQ_DONE flag that is set in scsi_softirq_done() > > from block soft_irq context that is used to signal when scsi_try_to_abort_cmd() should > > be calling __scsi_try_to_abort_cmd() for a timed out struct scsi_cmnd instead of > > returning SUCCESS via checking only blk_test_rq_complete(). This is done because > > blk_rq_timed_out_timer() calls blk_mark_rq_complete() before blk_rq_timed_out() -> > > struct request_queue->rq_timed_out_fn(). > > This is getting pretty far off into the weeds. I think the first step > should be queue lock push down into ->queuecommand. This would still > necessitate locking around the serial number. Hmmm, I am not sure I understand what you mean here. My understanding is that the whole point of the series was to remove any locking around the serial number in order to make scsi_dispatch_cmd() lockless, right..? That is what the current patch series already does, in that it makes the use of cmd->serial_number optional and requires LLDs who use this for anything beyond an informational purpose to explictly call scsi_cmd_get_serial(). > The next step might be > serial number elimination/reduction which might need to address issues > like this (or not ... block already knows the information, there's not > really much need for us to track it twice). There might also be other > lock aquisition reduction as part of step 2. > Correct, with this series cmd->serial_number still exists, but is completly optional and no longer used for any SCSI ML functionality. It remains used only beyond an information purpose by a handful of LLDs in their legacy error recovery handling, which have been updated in this series to explictly call scsi_cmd_get_serial(). So other than those handful special cases, all of the LLDs included in the series which explict set SHT->unlocked_qcmd=1 to run in scsi_dispatch_cmd() lockless mode will no longer need ->serial_number. --nab -- 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
