Re: Real-Time Preemption and RCU

[Thomas Gleixner]

On Sun, 2005-03-20 at 07:36 +0100, Manfred Spraul wrote:
> cpu 1:
> acquire random networking spin_lock_bh()
> 
> cpu 2:
> read_lock(&tasklist_lock) from process context
> interrupt. softirq. within softirq: try to acquire the networking lock.
> * spins.
> 
> cpu 1:
> hardware interrupt
> within hw interrupt: signal delivery. tries to acquire tasklist_lock.
> 
> --> deadlock.

Signal delivery from hw interrupt context (interrupt is flagged
SA_NODELAY) is not possible in RT preemption mode. The
local_irq_save_nort() check in __cache_alloc will catch you.

When it happens from a threaded irq handler the situation is solvable by
the PI code.

tglx


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