2.6.15-mm4 failure on power5

[Nathan Lynch]

Nathan Lynch wrote:
> Dave C Boutcher wrote:
> > On Tue, Jan 17, 2006 at 10:52:44AM -0600, Dave C Boutcher wrote:
> > > Well, it turns out that I've been running with CONFIG_DEBUG_MUTEXES all
> > > along...so no noise.  My console output is a little different that
> > > Serge's, so I think this is timing related.  Also note that I'm dying in
> > > the timer interrupt...
> > 
> > duh... here's the backtrace
> > 0:mon> t
> > [c000000000577890] c0000000000034b4 decrementer_common+0xb4/0x100
> > --- Exception: 901 (Decrementer) at c0000000004627ec
> > .__mutex_lock_interruptible_slowpath+0x3bc/0x4c4
> > [c000000000577c60] c000000000075064 .__lock_cpu_hotplug+0x44/0xa8
> > [c000000000577ce0] c000000000075600 .register_cpu_notifier+0x24/0x68
> > [c000000000577d70] c00000000052cd7c .do_init_bootmem+0x68c/0xab0
> > [c000000000577e50] c000000000522c84 .setup_arch+0x21c/0x2c0
> > [c000000000577ef0] c00000000051a538 .start_kernel+0x40/0x280
> > [c000000000577f90] c000000000008574 .hmt_init+0x0/0x8c
> 
> The mutex debug code (debug_spin_unlock in kernel/mutex-debug.h) is
> doing a local_irq_enable way before we're ready.

Looks like not only the powerpc setup_arch code could trigger this --
rcu_init, init_timers, and sched_init all do register_cpu_notifier
(and hence mutex_lock, therefore potentially enabling interrupts too
early in the mutex debug case) before the initial local_irq_enable in
start_kernel.