arm64, hw_breakpoint.c: Fix CPU hotplug callback registration
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 hw-breakpoint code in arm64 by using this latter form of callback registration. Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com> Cc: Ingo Molnar <mingo@kernel.org> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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@ -913,6 +913,8 @@ static int __init arch_hw_breakpoint_init(void)
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pr_info("found %d breakpoint and %d watchpoint registers.\n",
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core_num_brps, core_num_wrps);
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cpu_notifier_register_begin();
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/*
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* Reset the breakpoint resources. We assume that a halting
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* debugger will leave the world in a nice state for us.
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@ -927,7 +929,10 @@ static int __init arch_hw_breakpoint_init(void)
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TRAP_HWBKPT, "hw-watchpoint handler");
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/* Register hotplug notifier. */
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register_cpu_notifier(&hw_breakpoint_reset_nb);
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__register_cpu_notifier(&hw_breakpoint_reset_nb);
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cpu_notifier_register_done();
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/* Register cpu_suspend hw breakpoint restore hook */
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cpu_suspend_set_dbg_restorer(hw_breakpoint_reset);
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