Re: kernel page fult for a valid pointer?

On Mon, Aug 20, 2012 at 2:04 PM, John Baldwin <jhb@freebsd.org> wrote:
> On Saturday, August 18, 2012 2:29:26 pm Monthadar Al Jaberi wrote:
>> Hi,
>>
>> I am wondering is there a reason for getting "Fatal trap 12: page
>> fault while in kernel mode" "supervisor read, page not present" for an
>> address used to be valid in kernel space?
>>
>> I dont really understand why I am getting this, I added a hardware
>> watchpoint on the address, and when I got to the debuger I could read
>> the memory content and dump for that address. But when I continue from
>> the debugger I get the panic and now when I try to read the memory
>> content I get *** error reading from address ce733000 ***.
>
> Whatever memory was there might have been unmapped?  For example,
> memory pointed to by I/O buffers (struct buf/bio) use transient
> mappings that are only valid while an I/O request is in progress.

Thank you the for the reply, so if a struct gets freed will the page
it was on get un-mapped, so that I cant dump it in debugger? Even
VirtualBox debugger cant dump the memory giving
"VERR_PAGE_TABLE_NOT_PRESENT: Reading memory at...".

In my case it is a struct ieee80211_node which gets freed, but where
does the page get unmaped? I tried doubling the memory in VirtualBox.

br,

>
> --
> John Baldwin

-- 
Monthadar Al Jaberi
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