Re: suspicious RCU usage warnings in 3.3.0

[mroos@linux.ee]

> sparc64: Eliminate obsolete __handle_softirq() function
> 
> The invocation of softirq is now handled by irq_exit(), so there is no
> need for sparc64 to invoke it on the trap-return path.  In fact, doing so
> is a bug because if the trap occurred in the idle loop, this invocation
> can result in lockdep-RCU failures.  The problem is that RCU ignores idle
> CPUs, and the sparc64 trap-return path to the softirq handlers fails to
> tell RCU that the CPU must be considered non-idle while those handlers
> are executing.  This means that RCU is ignoring any RCU read-side critical
> sections in those handlers, which in turn means that RCU-protected data
> can be yanked out from under those read-side critical sections.
> 
> The shiny new lockdep-RCU ability to detect RCU read-side critical sections
> that RCU is ignoring located this problem.
> 
> The fix is straightforward: Make sparc64 stop manually invoking the
> softirq handlers.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

It works for me on Sun Fire V100 - no more RCU warnings under ping 
flood.

Tested-by: Meelis Roos <mroos@linux.ee>

-- 
Meelis Roos (mroos@linux.ee)