linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CA+55aFzVyTi_pR4y3=Z3y1bWkXbvgoJaykoyn0pUE7eTYgr+ZQ@mail.gmail.com>
Date:	Tue, 25 Nov 2014 21:52:37 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Juergen Gross <jgross@...e.com>
Cc:	"the arch/x86 maintainers" <x86@...nel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: frequent lockups in 3.18rc4

On Tue, Nov 25, 2014 at 9:24 PM, Juergen Gross <jgross@...e.com> wrote:
>
> Working on it. Triggering it via sysrq(l) isn't working: machine hung
> up. I'll try a dump, but this might take some time due to the machine
> size...

Actually, in that patch that did this:

-       pgd = pgd_offset(current->active_mm, address);
+       pgd = (pgd_t *)__va(read_cr3()) + pgd_index(address);

make the code do:

        pgd = (pgd_t *)__va(read_cr3()) + pgd_index(address);
        WARN_ON(pdg != pgd_offset(current->active_mm, address));

and now you should get a nice backtrace for exactly when it happens,
but it's on a working kernel, so nothing will lock up.

Hmm?

And leave it running for a while, and see if the trace is always the
same, or if there are variations on it...

Thanks,

                      Linus
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