On 3/17/2016 6:55 PM, Paul E. McKenney wrote:

The RCU stall-warn stack traces can be ugly, agreed.

That said, RCU used to use NMI-based stack traces, but switched to the
current scheme due to the NMIs having the unfortunate habit of locking
things up, which IIRC often meant no stack traces at all.  If I recall
correctly, one of the problems was self-deadlock in printk().

Steven Rostedt enabled the per_cpu printk func support in June 2014, and
the nmi_backtrace code uses it to just capture printk output to percpu
buffers, so I think it's going to be a lot more robust than earlier attempts.

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com