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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