Memory modified after free: Most recently used by acpitask
nate at root.org
Wed Nov 24 08:49:08 PST 2004
Gavin Atkinson wrote:
> Just got a panic on a 6-CURRENT (Thu Nov 18 16:36:35 GMT 2004) machine,
> while copying a large amount of data around.
> Seems to be an ACPI related reuse-after-free. As far as I can tell, 20
> bytes into the acpi_task structure is (int)ta_flags within the embedded
> struct task, but I can't see use of this field in the ACPI code so ACPI
> may be a red herring.
> Sadly, I don't have a core dump as the machine double faulted during the
> # cp -Rp /usr/* /var/usr
> [about 10 minutes later]
> Memory modified after free 0xc44a8420(28) val=0 @ 0xc44a8434
> panic: Most recently used by acpitask
Unfortunately, the panic message doesn't tell you who modified it since
someone with a stray pointer (say, who allocated/freed it before acpi)
could overwrite it and it was only detected on the next malloc. The way
I've found these is to boot -d (into ddb) and type "watch 0xc44a8420".
Then hit "c" to continue the boot. Dump a "tr" any time the watchpoint
triggers and look for suspicious callers.
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