Date: Mon, 20 Aug 2012 15:49:48 +0200 From: Monthadar Al Jaberi <monthadar@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: kernel page fult for a valid pointer? Message-ID: <CA%2BsBSo%2B_aYpYam31P_YhTnOMbLAZauVi-Qouz5AkdjeDCY22Sw@mail.gmail.com> In-Reply-To: <201208200804.31932.jhb@freebsd.org> References: <CA%2BsBSo%2BG7ovJk5O17YB-ZjCe%2BEQSntdx6MvBftKx9S=p4w8hvA@mail.gmail.com> <201208200804.31932.jhb@freebsd.org>
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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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