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    SubjectRe: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger 2.6.27-rc4 released
    Nick Piggin wrote:
    > On Thursday 21 August 2008 22:26, wrote:
    >> It's simple to reproduce. Take away the volatile declaration for the
    >> rlock_t structure in mdb-ia32.c (rlock_t debug_lock) in all code
    >> references and watch the thing lock up in SMP with multiple processors in
    >> the debugger each stuck with their own local copy of debug_lock.
    > You should disable preempt before getting the processor id. Can't see any
    > other possible bugs, but you should be able to see from the disassembly
    > pretty easily.

    debug_lock() is AFAICS only called from contexts which have preemption
    disabled. Last time around I recommended to Jeff to document this
    requirement on the calling context.

    But even though preemption is disabled, debug_lock() is still incorrect
    as I mentioned in my other post a minute ago. It corrupts its .flags
    and .count members. (Or maybe it coincidentally doesn't as long as
    volatile is around.)
    Stefan Richter
    -=====-==--- =--- =-=-=

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      Last update: 2008-08-21 16:13    [W:0.023 / U:17.040 seconds]
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