reliable "panic: isa_dmastart: bad bounce buffer"

Doug White dwhite at
Fri Apr 15 20:13:10 PDT 2005

On Tue, 12 Apr 2005, Mikhail Teterin wrote:

> Hello!
> Whenever I try to mount a floppy disk:
> 	 mount -t msdosfs /dev/fd0 /mnt
> I get:
> 	panic: isa_dmastart: bad bounce buffer
> The OS is FreeBSD-5.4-STABLE from last night, amd64. dmesg attached.

Probably related to:

fdc0: <floppy drive controller (FDE)> port 0x3f7,0x3f0-0x3f5 irq 6 drq 2
on acpi0
isa_dmainit(2, 40960) failed
fd0: <1440-KB 3.5" drive> on fdc0 drive 0

That message is printed by isa_dmainit() in src/sys/amd64/isa/isa_dma.c.
You might instrument that function and see where its blowing up.  I
suspect its getting the buffer from malloc() but the range check below it

Doug White                    |  FreeBSD: The Power to Serve
dwhite at          |

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