| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 29/51] arm64, debug-monitors: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:39:58 +0530 |
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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_maps_update_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_maps_update_done();
Fix the debug-monitors code in arm64 by using this latter form of callback registration.
Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Russell King <rmk+kernel@arm.linux.org.uk> Cc: linux-arm-kernel@lists.infradead.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
arch/arm64/kernel/debug-monitors.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index 636ba8b..959a16b 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -155,12 +155,16 @@ static struct notifier_block os_lock_nb = { static int debug_monitors_init(void) { + cpu_maps_update_begin(); + /* Clear the OS lock. */ smp_call_function(clear_os_lock, NULL, 1); clear_os_lock(NULL); /* Register hotplug handler. */ - register_cpu_notifier(&os_lock_nb); + __register_cpu_notifier(&os_lock_nb); + + cpu_maps_update_done(); return 0; } postcore_initcall(debug_monitors_init);
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