From mboxrd@z Thu Jan 1 00:00:00 1970 From: srivatsa.bhat@linux.vnet.ibm.com (Srivatsa S. Bhat) Date: Thu, 06 Feb 2014 03:39:58 +0530 Subject: [PATCH 29/51] arm64, debug-monitors: Fix CPU hotplug callback registration In-Reply-To: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> Message-ID: <20140205220957.19080.79200.stgit@srivatsabhat.in.ibm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 Cc: Will Deacon Cc: Russell King Cc: linux-arm-kernel at lists.infradead.org Signed-off-by: Srivatsa S. Bhat --- 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);