• Linus Torvalds's avatar
    [x86] Clean up MAXSMP Kconfig, and limit NR_CPUS to 512 · d25e26b6
    Linus Torvalds authored
    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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    d25e26b6
Kconfig 56.8 KB