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    SubjectRe: CONFIG_PREEMPT causes corruption of application's FPU stack
    Date
    On Sonntag, 1. Juni 2008, Andi Kleen wrote:
    > j.mell@t-online.de writes:
    > > or it is restored more than
    > > once. Please keep in mind, that I am always running two Einstein
    > > processes simultaneously on my two cores!
    > > I am willing to do further testing of this problem if someone can give
    > > me a hint how to continue.
    >
    > My bet would have been actually on
    > aa283f49276e7d840a40fb01eee6de97eaa7e012 because it does some nasty
    > things (enable interrupts in the middle of __switch_to).
    >
    > I looked through the old patchkit and couldn't find any specific
    > PREEMPT problems. All code it changes should run with preempt_off
    >
    > You could verify with sticking WARN_ON_ONCE(preemptible()) into
    > all the places acc207616a91a413a50fdd8847a747c4a7324167
    > changes (__unlazy_fpu, math_state_restore) and see if that triggers
    > anywhere.

    No, that did not trigger. I put the WARN_ON_ONCE into process.c, traps.c
    and also into the __unlazy_fpu macro in i387.h but I got no messages
    anywhere (dmesg, /var/log/messages, /var/log/warn) when the trap #8
    occurred.
    Meanwhile I am also running the tests on another machine to make sure it is
    not a hardware-related problem.

    Any new ideas are welcome!

    Meanwhile I will go back to 2.6.20 and revert
    aa283f49276e7d840a40fb01eee6de97eaa7e012. Maybe I got on a wrong track...

    Bye,
    Jürgen
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