Messages in this thread | | | Date | Tue, 4 Dec 2012 21:05:29 -0800 | From | Frank Rowand <> | Subject | Re: [PATCH RT 0/2][RFC] fix RCU stall warning on ARM |
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On 12/04/12 20:47, Frank Rowand wrote: > The RCU stall warning functions call trigger_all_cpu_backtrace() > to print a backtrace on each cpu. This function is only > implemented for x86. Add a version for ARM. > > With CONFIG_PREEMPT_RT_FULL enabled, flushing the output from > printk() is inhibited in some contexts to avoid increasing > real time latencies. The RCU stall warnings are inhibited > on ARM due to this feature. (I have not tested whether this > is also the case on other architectures.) Add back the > oops_in_progress flag to allow the RCU stall warnings to > print immediately.
When I first implemented these patches on a locally modified 3.0.27-rt67, the call to "bust_spinlocks(0)" that I added to print_cpu_stall() led to LOCKDEP warning of inconsistent lock state from a trylock in serial_omap_console_write():
else if (oops_in_progress) locked = spin_trylock_irqsave(&up->port.lock, flags);
If I understand correctly, the warning is triggered on the slow lock path. Some more of the warning is:
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage. swapper/1/0 [HC1[1]:SC0[0]:HE0:SE1] takes: (&(&(&port->lock)->lock)->wait_lock){?.+...}, at: [<c0478ed0>] rt_spin_trylock_irqsave+0x24/0xe0
...
other info that might help us debug this: Possible unsafe locking scenario:
CPU0 ---- lock(&(&(&port->lock)->lock)->wait_lock); <Interrupt> lock(&(&(&port->lock)->lock)->wait_lock);
I have not been able to trigger the warning on recent versions of the patches, but I suspect the latent problem might still exist.
-Frank
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