kernel panic with 29160 when doing tape backup

[Nick Pasich]

On Mon, Nov 26, 2001 at 08:08:27AM -0700, Justin T. Gibbs wrote:
> > The panic message: 
> >
> >          kernel panic: Too few segs for dma mapping.  Increase AHC_NSEG
> >
> >  
> > I recompiled the kernel after increasing the AHC_NSEG's to 512 in
> > aic7xxx_osm.h, but that didn't help.
> >
> > Not having a clue as to what the problem was, I started rebooting with
> > older kernels. I tried 2.4.14-pre8, 2.4.13-ac4, 2.4.12-ac5 and
> > 2.4.10-ac12.  All of them gave the same panic message....
> >
> > I finally tried 2.4.7, which gave me an error message, but completed
> > the backup.
> >
> > The error message for 2.4.7:
> >
> >      Saw underflow (4096 of 4096 bytes). Treated as error
> >      Saw underflow (4096 of 4096 bytes). Treated as error
> >      Saw underflow (4096 of 4096 bytes). Treated as error
> >      Saw underflow (4096 of 4096 bytes). Treated as error
> >      Saw underflow (4096 of 4096 bytes). Treated as error
> >      Saw underflow (4096 of 4096 bytes). Treated as error
> >      SCSI disk error : host 0 channel 0 id 0 lun 0 return code = 70000
> >       I/O error: dev 08:01, sector 59591
> 
> I guess that the msdos file-system code in 2.4.7 does not have whatever
> bug it is that causes the kernel to attempt an I/O that violates the
> exported limit on the segment list set by the aic7xxx driver.  If you
> upgrade your 2.4.7 kernel to use the latest aic7xxx driver, you'll probably
> have a stable system.  Patches against 2.4.7 can be found here:
> 
> http://people.FreeBSD.org/~gibbs/linux/
> 
> You might be able to track down the root cause of the bug by providing
> a stack trace from the panic you see when dumping an msdos file system.
> I guarantee you though, it is not the aic7xxx driver's fault.
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> --
> Justin

 Justin,

 I have now upgraded to Linux Kernel version 2.4.16 and the same
 system lockup problem exists when doing a msdos partition backup to 
 a scsi tape.

 The panic message: 
     kernel panic: Too few segs for dma mapping.  Increase AHC_NSEG

 I have another Linux Computer running the same kernel (2.4.16) that
 has no problems at all. The difference being the scsi adapter is a
 BusLogic Model BT-958 PCI Wide Ultra SCSI Host Adapter.

 I have replaced the contents of /usr/src/linux/drivers/scsi/aic7xxx
 directory (AIC7XXX_DRIVER_VERSION  "6.2.4"),
 with the code from linux-2.4.7 (AIC7XXX_DRIVER_VERSION  "6.1.13").

 I now can now do a successful backup of an msdos partition with a 
 couple of "kernel: Saw underflow (4096 of 4096 bytes). Treated as error"
 messages with no lockup.

 This is obviously a driver problem, as the only difference in the
 kernels is the code in the aic7xxx directory.....

 AIC7XXX_DRIVER_VERSION  "6.2.4" causes kernel panic lockups..

 AIC7XXX_DRIVER_VERSION  "6.1.13" reports underflows and continues
 running....

 If you have a msdos partition available, you might want to try a test
 backup to a scsi dat tape and see if you have the same problem.......

                  Thanks for your time,

                  ---( Nick Pasich )---


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