powerpc: Make the irq reverse mapping radix tree lockless
The radix trees used by interrupt controllers for their irq reverse mapping (currently only the XICS found on pSeries) have a complex locking scheme dating back to before the advent of the lockless radix tree. This takes advantage of the lockless radix tree and of the fact that the items of the tree are pointers to a static array (irq_map) elements which can never go under us to simplify the locking. Concurrency between readers and writers is handled by the intrinsic properties of the lockless radix tree. Concurrency between writers is handled with a global mutex. Signed-off-by: Sebastien Dugue <sebastien.dugue@bull.net> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Michael Ellerman <michael@ellerman.id.au> Signed-off-by: Paul Mackerras <paulus@samba.org>
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