Commit ee1238a1 authored Feb 14, 2014 by Srivatsa S. Bhat Committed by Osvaldo Banuelos Jul 01, 2014

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>
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: 3d0dc643f81ed64e2a7f839e8491728addbc51b9
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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

parent 6f52528e

arch/arm64/kernel/hw_breakpoint.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -913,6 +913,8 @@ static int __init arch_hw_breakpoint_init(void)
		pr_info("found %d breakpoint and %d watchpoint registers.\n",
		core_num_brps, core_num_wrps);

		cpu_notifier_register_begin();

		/*
		* Reset the breakpoint resources. We assume that a halting
		* debugger will leave the world in a nice state for us.
		@@ -927,7 +929,10 @@ static int __init arch_hw_breakpoint_init(void)
		TRAP_HWBKPT, "hw-watchpoint handler");

		/* Register hotplug notifier. */
		register_cpu_notifier(&hw_breakpoint_reset_nb);
		__register_cpu_notifier(&hw_breakpoint_reset_nb);

		cpu_notifier_register_done();

		/* Register cpu_suspend hw breakpoint restore hook */
		cpu_suspend_set_dbg_restorer(hw_breakpoint_reset);