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SubjectRe: [PATCH] do_wp_page: BUG on invalid pfn
On Fri, Aug 15, 2003 at 05:52:09PM -0400, Ed L Cashin wrote:
> Mike Fedyk <mfedyk@matchmail.com> writes:
>
> > On Fri, Aug 15, 2003 at 05:15:45PM -0400, Ed L Cashin wrote:
> >> Rusty Russell <rusty@rustcorp.com.au> writes:
> >>
> >> > In message <87d6fixvpm.fsf@uga.edu> you write:
> >> >> This patch just does what the comment says should be done.
> >> >
> >> > Hi Ed!
> >> >
> >> > Not trivial I'm afraid. Send to Linus and lkml.
> >>
> >>
> >> This patch just does what the comment says should be done. I thought
> >> it was a trivial patch, but Rusty Russell has informed me otherwise.
> >> (Thanks, RR).
> >>
> >>
> >> --- linux-2.6.0-test2/mm/memory.c.orig Sun Jul 27 13:01:24 2003
> >> +++ linux-2.6.0-test2/mm/memory.c Wed Aug 6 18:30:55 2003
> >> @@ -990,15 +990,10 @@
> >> int ret;
> >>
> >> if (unlikely(!pfn_valid(pfn))) {
> >> - /*
> >> - * This should really halt the system so it can be debugged or
> >> - * at least the kernel stops what it's doing before it corrupts
> >> - * data, but for the moment just pretend this is OOM.
> >> - */
> >> - pte_unmap(page_table);
> >> printk(KERN_ERR "do_wp_page: bogus page at address %08lx\n",
> >> address);
> >> - goto oom;
> >> + dump_stack();
> >> + BUG();
> >
> > You're not unmapping the pte I guess to not interfere with the dump_stack,
>
> This patch changes the logic from "pretend it's out of memory" to
> "announce something's very wrong and bail out right away." Unmapping
> the pte seems like a precursor to carrying on business as usual, but
> there must be some subtleties here that I am unaware of, or Rusty
> Russell wouldn't have called this patch non-trivial.

So does show_stack() halt the kernel? If not, then you probably want the
pte_unmap since you'll have a working/semi-working system after the bug()
call.

And if show_stack() does halt the kernel, what's the point of bug() then?
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