Messages in this thread | | | Date | Thu, 21 Aug 2008 16:09:09 +0200 | From | Stefan Richter <> | Subject | Re: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger 2.6.27-rc4 released |
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Nick Piggin wrote: > On Thursday 21 August 2008 22:26, jmerkey@wolfmountaingroup.com 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 -=====-==--- =--- =-=-= http://arcgraph.de/sr/
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