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    SubjectRe: Buggy IPI and MTRR code on low memory

    On Wed, 28 Jan 2009, Peter Zijlstra wrote:

    > On Wed, 2009-01-28 at 12:24 -0500, Steven Rostedt wrote:
    > > On Wed, 28 Jan 2009, Peter Zijlstra wrote:
    > > > ---
    > > > Subject: x86: fix potential deadlock in set_mtrr()
    > > > From: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > > > Date: Wed Jan 28 17:17:32 CET 2009
    > > >
    > > > smp_call_function() can fall-back to waiting on completion in case of
    > > > low memory (GFP_ATOMIC). set_mtrr() relies on the async behaviour of !wait.
    > > >
    > > > This would deadlock.
    > > >
    > > > Fix this by providing per-cpu csd's and using __smp_call_function_single().
    > >
    > > I applied the patch but it still locked up in the testing NMI
    > > watchdog code. Not saying your patch is at fault, because we never made it
    > > to your code. This is probably not an issue, since if we have low memory
    > > at bootup, we have much bigger problems to deal with.
    > >
    > > I'll have skip the NMI test and see if it locks up any place else.
    >
    > Right, the NMI code does exactly the same, in that case your patch might
    > well be the best way forward.

    Is there any reason to force the user to have to deal with a wait? We can
    add this code to handle the failed alloc case, and I can even make it a
    bit better to only do the copy *d = data; when the RELEASE flag is set.

    -- Steve



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