Luben Tuikov wrote: > --- 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 ^^^^^^^^^^^^^ Luben, The failure being reported is that the block layer SG_IO ioctl already does what you are proposing to do for the sg driver. Hence an application, cdparanoia in this case, since it coded against documented behaviour, assumes that SG_DXFER_TO_FROM_DEV will read from the device. See the definition of SG_DXFER_TO_FROM_DEV in sg.h and the document above. So your proposed patch would compound the problem. The solution is _not_ to change the sg driver and put the equivalent of the reverse of your patch in the block layer SG_IO ioctl. There is nothing to stop a new direction flag being added called SG_DXFER_BIDIRECTIONAL that maps to DMA_BIDIRECTIONAL. Doug Gilbert - 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
