| Message ID | 20140205220654.19080.11341.stgit@srivatsabhat.in.ibm.com (mailing list archive) |
|---|---|
| State | Awaiting Upstream, archived |
| Headers | show |
On Thursday 06 February 2014 03:36 AM, Srivatsa S. Bhat wrote: > 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. Acked-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com> > > 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 */ >
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 */
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(-)