Commit 6f52528e authored Feb 14, 2014 by Srivatsa S. Bhat Committed by Osvaldo Banuelos Jul 01, 2014

arm, hw-breakpoint: 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 arm by using this latter form of callback
registration.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Git-commit: c5929bd3a9920432dfb485253c64163fdfc90faf
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>

parent cbad9f58

arch/arm/kernel/hw_breakpoint.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -1094,6 +1094,8 @@ static int __init arch_hw_breakpoint_init(void)
		core_num_brps = get_num_brps();
		core_num_wrps = get_num_wrps();

		cpu_notifier_register_begin();

		/*
		* We need to tread carefully here because DBGSWENABLE may be
		* driven low on this core and there isn't an architected way to
		@@ -1110,6 +1112,7 @@ static int __init arch_hw_breakpoint_init(void)
		if (!cpumask_empty(&debug_err_mask)) {
		core_num_brps = 0;
		core_num_wrps = 0;
		cpu_notifier_register_done();
		return 0;
		}

		@@ -1129,7 +1132,10 @@ static int __init arch_hw_breakpoint_init(void)
		TRAP_HWBKPT, "breakpoint debug exception");

		/* Register hotplug and PM notifiers. */
		register_cpu_notifier(&dbg_reset_nb);
		__register_cpu_notifier(&dbg_reset_nb);

		cpu_notifier_register_done();

		pm_init();
		return 0;
		}