| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 13/51] powerpc, sysfs: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:36:54 +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 sysfs code in powerpc by using this latter form of callback registration.
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com> Cc: Olof Johansson <olof@lixom.net> Cc: Wang Dongsheng <dongsheng.wang@freescale.com> Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
arch/powerpc/kernel/sysfs.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c index 97e1dc9..c29ad44 100644 --- a/arch/powerpc/kernel/sysfs.c +++ b/arch/powerpc/kernel/sysfs.c @@ -975,7 +975,8 @@ static int __init topology_init(void) int cpu; register_nodes(); - register_cpu_notifier(&sysfs_cpu_nb); + + cpu_maps_update_begin(); for_each_possible_cpu(cpu) { struct cpu *c = &per_cpu(cpu_devices, cpu); @@ -999,6 +1000,11 @@ static int __init topology_init(void) if (cpu_online(cpu)) register_cpu_online(cpu); } + + __register_cpu_notifier(&sysfs_cpu_nb); + + cpu_maps_update_done(); + #ifdef CONFIG_PPC64 sysfs_create_dscr_default(); #endif /* CONFIG_PPC64 */
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