[Crash-utility] WARNING: cannot access vmalloc'd module memory

[Dave Anderson]

Mike Mason wrote:

> I'm seeing the following warning when I run crash against a kdump vmcore
>   created on an i386 smp system with 4 GB RAM.
>
>         WARNING: cannot access vmalloc'd module memory
>
> The relevant version #s are:
>
>         crash 4.0-25
>         kernel 2.6.16.14-6-bigsmp
>
> crash -d2 shows the following:
>
> crash: read error: kernel virtual address: f8c6f680  type: "module struct"
> WARNING: cannot access vmalloc'd module memory

Hi Mike,

It's a read error, and given that netdump/diskdump/kdump all use the
same "read_netdump()" function, if the physical address associated
with vmalloc address f8c6f680 is not found in the vmcore file, a read
error like the above will occur.

However, that does presume that the virtual-to-physical translation
of the module's vmalloc'd address is correct.  If you run crash on the
live system running that particular kernel, is module data accessible?

Also, if you do a "vtop f8c6f680", it will give you the physical address
that would be passed to read_netdump() to access.  You can then
check that physical address against the ranges of physical memory
stored in the vmcore by doing a "help -n".

Dave