[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 <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>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 68d91c8233f42162039af96c8ed1fdd3e1d6a88e..ed92864d1325c09092f3e8ed4918f26341f23161 100644 (file)
--- 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 IOMMU_HELPER
        def_bool (CALGARY_IOMMU || GART_IOMMU || SWIOTLB || AMD_IOMMU)

+

 config MAXSMP
        bool "Configure Maximum number of SMP Processors and NUMA Nodes"
 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.
 
        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
 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
        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
        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.
          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"
 
 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.
 
          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
 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
        range 1 9   if X86_64

+       default "9" if MAXSMP

        default "6" if X86_64
        default "4" if X86_NUMAQ
        default "3"
        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.
        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
 
 config HAVE_ARCH_BOOTMEM_NODE
        def_bool y