Messages in this thread | | | Date | Wed, 17 Nov 2010 10:11:19 -0500 | From | Jeff Garzik <> | Subject | Re: [PATCH] libata: remove unlock+relock cycle in ata_scsi_queuecmd |
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On 11/17/2010 05:01 AM, Tejun Heo wrote: > Hello, Jeff, Linus. > > On 11/17/2010 09:08 AM, Jeff Garzik wrote: >> Looking solely at the SCSI code (ie. ignoring LLD code), it seems >> like the magic number zero for serial_number is signaling a boolean >> condition "are we an EH command?" >> >> EH tests this at the very beginning of the abort/reset/explode error >> handling sequence, presumably to avoid recursive EH invocations >> (scsi_try_to_abort_cmd). >> >> So maybe an EH expert (Tejun?) can correct me here, but I think we >> may be able to completely the lock/get-serial/unlock sequence from >> libata, as long as scsi_init_cmd_errh() reliably sets an "I am an EH >> command" flag. >> >> Would be nice if true... > > Yeah, it's actually nice (for once). libata doesn't use or care about > scmd->serial_number at all. The SCSI EH path you mentioned above is > not applicable as libata implements its eh_strategy_handler and SCSI > only calls scsi_try_to_abort_cmd() for the default EH handler, > scsi_unjam_host(). > > We'll need to test a bit to make sure everything is okay but I'm > fairly certain removing it won't break anything fundamental. If > something breaks at all, it would be some silly easy-to-fix thing.
It would be surprising if there is breakage, because serial_number is only tested in two places in the generic kernel:
scsi_cmd_get_serial() -- where it simply avoids the zero value -- and scsi_try_to_abort_cmd().
Jeff
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