--- Douglas Gilbert <dougg@xxxxxxxxxx> wrote: > Tejun Heo wrote: > > [CC'ing Monty and Douglas.] > > > > Hello, the original thread can be read from the following URL. > > > > http://thread.gmane.org/gmane.linux.ide/13708/focus=13708 > > > > Brice Goglin wrote: > >> ens Axboe wrote: > >>> On Mon, Oct 30 2006, Gregor Jasny wrote: > >>> > >>>> 2006/10/30, Jens Axboe <jens.axboe@xxxxxxxxxx>: > >>>> > >>>>> Can you confirm that 2.6.18 works? > >>>>> > >>>> The reporter of [1] states that his SATA Thinkpad freezes with 2.6.17 > >>>> and 2.6.18, too. > >>>> > >>>> Gregor > >>>> > >>>> [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=391901 > >>>> > >>> Ok, mainly just checking if this was a potential dupe of another bug. > >>> > >>> > >> > >> Jens (or anybody else who has any idea of how to debug this), > >> > >> Did you have a chance to reproduce the problem? I guess we "only" need a > >> machine with SATA/ata_piix and cdparanoia 3.10. If you want me to debug > >> some stuff, feel free to tell me what. But, since it freezes the machine > >> and sysrq doesn't even work, I don't really know what to try... > >> > >> I just tried on rc5 and rc5-mm1, both have the problem (as 2.6.16, .17 > >> and .18 do, don't know about earlier kernels). I didn't have a audio CD > >> here, so I tried abcde on a DVD on purpose. With cdparanoia 3.10-pre0 > >> (from Debian testing), it reports nothing during about 5 seconds and > >> then the machine freezes. With cdparanoia 3a9.8-11 (from Debian stable), > >> it reports an error very quickly, and dmesg gets a couple line like > >> these: > >> sg_write: data in/out 12/12 bytes for SCSI command 0x43--guessing > >> data in; > >> program cdparanoia not setting count and/or reply_len properly > > > > Okay, here's the story. > > > > In interface/scan_devices.c::cdda_identify_scsi(), cdparanoia calls > > scsi_inquiry() to identify the device and determine interface type. This > > seems to be the first time to actually issue commands to the device. As > > interface type isn't completely determined, for sg devices, it first > > issues the command w/ d->interface set to SGIO_SCSI. If that fails, it > > falls back to SGIO_SCSI_BUGGY1. > > > > For to-device request, both SGIO_SCSI and SGIO_SCSI_BUGGY1 set > > sg_io_hdr.dxfer_direction to SG_DXFER_TO_DEV. But for from-device > > request, SGIO_SCSI uses SG_DXFER_TO_FROM_DEV while SGIO_SCSI_BUGGY1 uses > > SG_DXFER_FROM_DEV. So, cdparanoia first issues inquiry w/ > > SG_DXFER_TO_FROM_DEV and if that fails falls back to SG_DXFER_FROM_DEV. > > > > drivers/scsi/sg.c interprets SG_DXFER_TO_FROM_DEV as read while > > block/scsi_ioctl.c interprets it as write. I guess this is historic > > thing (scsi/sg.c updated but block/scsi_ioctl.c is forgotten). As > > written above, cdparanoia can handle both cases as long as the kernel > > promptly fails command issued with the wrong direction. > > > > This works for most PATA ATAPI devices. Most devices detect reversed > > transfer and terminate the command promptly. But this doesn't seem to > > be true for SATA device. Many just hang and time out commands with the > > wrong transfer direction. If you consider that most early SATA ATAPI > > devices are actually PATA + bridge, this is sorta inevitable. The > > PATA-SATA bridge cannot issue D2H FIS to abort the command by itself. > > It's just mirroring the status of PATA side and PATA side doesn't know > > SATA protocol mismatch has occurred. > > > > So, IDENTIFY w/ write-DMA protocol times out after quite some seconds. > > This is where things go worse from bad. SATA controllers which have > > shadow TF registers don't handle timeout conditions very well, > > especially when they're waiting for data transfer. They basically hold > > the PCI bus and hang till the transfer completes (which never happens). > > That's where the hard lock up comes from. > > > > Jens, I think we need to match block sg's behavior to SCSI's. Monty, > > the timeout and hard lock up are due to hardware restrictions. Kernel > > and libata can't do much about it. So, please find other way to detect > > interface. > > Tejun, > Your SG_DXFER_TO_FROM_DEV analysis is correct. > > The stupid ~!@# who wrote the code, and the documentation > for it, defined SG_DXFER_TO_FROM_DEV to mean a "transfer > from device" operation where the kernel buffer receiving > the DMA transfer was prefilled with data that the application > provided. That certainly isn't a bidirectional transfer to/from > the device, but it is a bidirectional transfer to kernel > buffers when indirect IO is used. > > Why do this? Because the 'resid' field indicating how much > less data was transferred in a "from_device" transfer than > was requested, was not added to SCSI infrastructure till much > later. There are still LLDs out there that don't implement it. > It also reflected a similar technique used with the sg_header > structure (circa 1992) for precisely the same reason. And > application writers wanted that functionality. Joerg was the > first name of one such application writer. > > > Coincidentally I am sitting on a patch from Luben Tuikov > to cause the same breakage in the sg driver itself. Here is a link to the recently posted 8 month patch: http://marc.theaimsgroup.com/?l=linux-scsi&m=116267031029025&w=2 The patch would appear to fix the problem Tejun is describing. I cannot quite remember exactly what I was doing that day 8 months ago, but was either disk or tape devices testing and arrived at that patch. This patch had been in my dev (gateway) tree for the last 8 months, without any problems. Luben > Nobody has proposed a patch to the documentation for > the explanation of SG_DXFER_TO_FROM_DEV :-) > http://www.torque.net/sg/p/sg_v3_ho.html > > > As I am currently proposing a SCSI pass through version 4 > interface with twin scatter gather lists for independent > bidirectional transfers for SCSI commands, I'm not sure > what setting DMA_BIDIRECTIONAL in the existing interface > buys us. > > > When you maintain and document a pass through interface you > sit between two groups of people that have conflicting goals > and don't have a particularly high opinion of each other. > > Doug Gilbert > > > - > To unsubscribe from this list: send the line "unsubscribe linux-ide" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > - 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
