Messages in this thread | | | Date | Tue, 05 Feb 2002 23:40:22 -0500 | From | Douglas Gilbert <> | Subject | Re: one-line-patch against SCSI-Read-Error-BUG() |
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Jens Axboe wrote: > > On Tue, Feb 05 2002, Ralf Oehler wrote: > > Hi, List > > > > I think, I found a very simple solution for this annoying BUG(). > > You fail to understand that the BUG triggering indicates that their is a > BUG _somewhere_ -- the triggered BUG is not the bug itself, of course, > that would be stupid :-) > > > Since at least kernel 2.4.16 there is a BUG() in pci.h, > > that crashes the kernel on any attempt to read a SCSI-Sector > > from an erased MO-Medium and on any attempt to read > > a sector from a SCSI-disk, which returns "Read-Error". > > > > There seems to be a thinko in the corresponding code, which > > does not take into account the case where a SCSI-READ > > does not return any data because of a "sense code: read error" > > or a "sense code: blank sector". > > > > I simply commented out this BUG() statement (see below) > > and everything worked well from there on. The BUG() > > seems to be inadequate. > > The BUG is dangerous, because it means mapping DMA to a 0 address (plus > offset). Naturally there is no way in hell your "fix" will be applied, > since it a pretty bad bandaid. > > A safer solution for you right now would be to just terminate the > mapping when you encounter this. So something ala > > if (!sg[i].page && !sg[i].address) > return i; > > That's not a bug fix either, but at least it's safer than your version. > Stock kernel won't be patched until the real problem is found, though.
Jens, The sg driver was tripping that BUG() and I have submitted a patch for that. However Ralf probably wasn't using sg to read his MO disk.
There are several uses of "sgpnt[i].address" in scsi_lib.c that you might like to look at. Can't see any other uses in sd, sr or the mid level. Another possibility is a missing memset or explicit NULL initialisation on a scatterlist array.
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