| Message ID | 20140205220957.19080.79200.stgit@srivatsabhat.in.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Feb 05, 2014 at 10:09:58PM +0000, 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: [...] > 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); Acked-by: Will Deacon <will.deacon@arm.com> Will
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);
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(-)