• Srivatsa S. Bhat's avatar
    oprofile, nmi-timer: Fix CPU hotplug callback registration · 180d8646
    Srivatsa S. Bhat authored
    Subsystems that want to register CPU hotplug callbacks, as well as perform
    initialization for the CPUs that are already online, often do it as shown
    below:
    
    	get_online_cpus();
    
    	for_each_online_cpu(cpu)
    		init_cpu(cpu);
    
    	register_cpu_notifier(&foobar_cpu_notifier);
    
    	put_online_cpus();
    
    This is wrong, since it is prone to ABBA deadlocks involving the
    cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
    with CPU hotplug operations).
    
    Instead, the correct and race-free way of performing the callback
    registration is:
    
    	cpu_notifier_register_begin();
    
    	for_each_online_cpu(cpu)
    		init_cpu(cpu);
    
    	/* Note the use of the double underscored version of the API */
    	__register_cpu_notifier(&foobar_cpu_notifier);
    
    	cpu_notifier_register_done();
    
    Fix the nmi-timer code in oprofile by using this latter form of callback
    registration.
    
    Cc: Robert Richter <rric@kernel.org>
    Cc: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: default avatarSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    180d8646
nmi_timer_int.c 3.47 KB