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[x86] Clean up MAXSMP Kconfig, and limit NR_CPUS to 512
This fixes a regression that was indirectly caused by commit 1184dc2f ("x86: modify Kconfig to allow up to 4096 cpus"). Allowing 4k CPU's is not practical at this time, because we still have a number of places that have several 'cpumask_t's on the stack, and a 4k-bit cpumask is 512 bytes of stack-space for each such variable. This literally caused functions like 'smp_call_function_mask' to have a 2.5kB stack frame, and several functions to have 2kB stackframes. With an 8kB stack total, smashing the stack was simply much too likely. At least bugzilla entry http://bugzilla.kernel.org/show_bug.cgi?id=11342 was due to this. The earlier commit to not inline load_module() into sys_init_module() fixed the particular symptoms of this that Alan Brunelle saw in that bugzilla entry, but the huge stack waste by cpumask_t's was the more direct cause. Some day we'll have allocation helpers that allocate large CPU masks dynamically, but in the meantime we simply cannot allow cpumasks this large. Cc: Alan D. Brunelle <Alan.Brunelle@hp.com> Cc: Mike Travis <travis@sgi.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by:Linus Torvalds <torvalds@linux-foundation.org>