RT and Signals

[Daniel Walker <dwalker@mvista.com>]

	I'm not sure if this has changed at all in recent RT patches, but I've
noticed several issues popping up that are related to the timer
interrupt sending signals , one in particular is the fact that
send_sig() calls into __cache_alloc() which has it's interrupt disable
protections removed in RT . I've observed slab corruption due to this
while running lmbench and LTP .

	Another issue was a livelock related to the timer interrupt calling
send_sig which locks tasklist_lock and siglock , which are both mutexes
(deadlock detect was on , but didn't trigger).. 

	LTP and lmbench seem to bring all these issues to the surface, but they
are all different depending on the architecture. I've been treating the
symptoms , but not the disease .. Ultimately , we need some protections,
in signal deliver, to stop the timer interrupt .. 

Daniel