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    acpi-cpufreq: fix 'smp_call_function_many()' confusion · ea34f43a
    Linus Torvalds 提交于
    It turns out that 'smp_call_function_many()' doesn't work at all like
    'smp_call_function_single()', and my change to Andrew's patch to use it
    rather than a loop over all CPU's acpi-cpufreq doesn't work.
    
    My bad.
    
    'smp_call_function_many()' has two "features" (aka "documented bugs"):
    
     (a) it needs to be called with preemption disabled, because it uses
         smp_processor_id() without guarding the CPU lookup with 'get_cpu()'
         and 'put_cpu()' like the 'single' variant does.
    
     (b) even if the current CPU is part of the CPU mask, it won't do the
         call on that CPU.
    
    Still, we're better off trying to use 'smp_call_function_many()' than
    looping over CPU's, since it at least in theory allows us to use a
    broadcast IPI and do it all in parallel.  So let's just work around the
    silly semantic bugs in that function.
    Reported-and-tested-by: NAli Gholami Rudi <ali@rudi.ir>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Andrew Morton <akpm@linux-foundation.org>,
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: Dave Jones <davej@redhat.com>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    ea34f43a
acpi-cpufreq.c 21.1 KB