From: Linus Torvalds Date: Mon, 25 Aug 2008 21:15:38 +0000 (-0700) Subject: [x86] Clean up MAXSMP Kconfig, and limit NR_CPUS to 512 X-Git-Tag: v2.6.27-rc5~32 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d25e26b61d59370eee8b7f2634641eb0fa76e952;p=linux-2.6 [x86] Clean up MAXSMP Kconfig, and limit NR_CPUS to 512 This fixes a regression that was indirectly caused by commit 1184dc2ffe2c8fb9afb766d870850f2c3165ef25 ("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 Cc: Mike Travis Cc: Ingo Molnar Cc: Thomas Gleixner Signed-off-by: Linus Torvalds --- diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 68d91c8233..ed92864d13 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -577,35 +577,29 @@ config SWIOTLB config IOMMU_HELPER def_bool (CALGARY_IOMMU || GART_IOMMU || SWIOTLB || AMD_IOMMU) + config MAXSMP bool "Configure Maximum number of SMP Processors and NUMA Nodes" - depends on X86_64 && SMP + depends on X86_64 && SMP && BROKEN default n help Configure maximum number of CPUS and NUMA Nodes for this architecture. If unsure, say N. -if MAXSMP -config NR_CPUS - int - default "4096" -endif - -if !MAXSMP config NR_CPUS - int "Maximum number of CPUs (2-4096)" - range 2 4096 + int "Maximum number of CPUs (2-512)" if !MAXSMP + range 2 512 depends on SMP + default "4096" if MAXSMP default "32" if X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000 default "8" help This allows you to specify the maximum number of CPUs which this - kernel will support. The maximum supported value is 4096 and the + kernel will support. The maximum supported value is 512 and the minimum value which makes sense is 2. This is purely to save memory - each supported CPU adds approximately eight kilobytes to the kernel image. -endif config SCHED_SMT bool "SMT (Hyperthreading) scheduler support" @@ -996,17 +990,10 @@ config NUMA_EMU into virtual nodes when booted with "numa=fake=N", where N is the number of nodes. This is only useful for debugging. -if MAXSMP - config NODES_SHIFT - int - default "9" -endif - -if !MAXSMP -config NODES_SHIFT - int "Maximum NUMA Nodes (as a power of 2)" + int "Maximum NUMA Nodes (as a power of 2)" if !MAXSMP range 1 9 if X86_64 + default "9" if MAXSMP default "6" if X86_64 default "4" if X86_NUMAQ default "3" @@ -1014,7 +1001,6 @@ config NODES_SHIFT help Specify the maximum number of NUMA Nodes available on the target system. Increases memory reserved to accomodate various tables. -endif config HAVE_ARCH_BOOTMEM_NODE def_bool y