On Thu, Feb 06, 2014 at 07:41:03PM +0100, Oleg Nesterov wrote: > On 02/06, Srivatsa S. Bhat wrote: > > > > The following method of CPU hotplug callback registration is not safe > > due to the possibility of an ABBA deadlock involving the cpu_add_remove_lock > > and the cpu_hotplug.lock. > > Off-topic, but perhaps it also makes sense to add the lockdep annotations > later, to catch other similar problems. Currently get_online_cpus() acquires > nothing from lockdep pov.
Well, both get/put_online_cpus() as well as cpu_hotplug_begin/end() take the cpu_hotplug.lock mutex. So ideally the lockdep annotations of mutex_lock/unlock() should have worked. If it hasn't, then the following lockdep annotations to cpu-hotplug locking should do the trick. Signed-off-by: Gautham R. Shenoy <[email protected]> --- kernel/cpu.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/kernel/cpu.c b/kernel/cpu.c index deff2e6..3d2dd1c 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -19,6 +19,7 @@ #include <linux/mutex.h> #include <linux/gfp.h> #include <linux/suspend.h> +#include <linux/lockdep.h> #include "smpboot.h" @@ -57,21 +58,34 @@ static struct { * an ongoing cpu hotplug operation. */ int refcount; + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif } cpu_hotplug = { .active_writer = NULL, .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock), .refcount = 0, +#ifdef CONFIG_DEBUG_LOCK_ALLOC + .dep_map = {.name = "cpu_hotplug.lock" }, +#endif }; +#define cphp_lock_acquire_read(l, s, t, i) lock_acquire_shared_recursive(l, s, t, NULL, i) +#define cphp_lock_acquire(l, s, t, i) lock_acquire_exclusive(l, s, t, NULL, i) +#define cphp_lock_release(l, n, i) lock_release(l, n, i) + void get_online_cpus(void) { might_sleep(); if (cpu_hotplug.active_writer == current) return; + cphp_lock_acquire_read(&cpu_hotplug.dep_map, 0, 0, _RET_IP_); mutex_lock(&cpu_hotplug.lock); cpu_hotplug.refcount++; mutex_unlock(&cpu_hotplug.lock); + } EXPORT_SYMBOL_GPL(get_online_cpus); @@ -79,6 +93,7 @@ void put_online_cpus(void) { if (cpu_hotplug.active_writer == current) return; + mutex_lock(&cpu_hotplug.lock); if (WARN_ON(!cpu_hotplug.refcount)) @@ -87,6 +102,7 @@ void put_online_cpus(void) if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) wake_up_process(cpu_hotplug.active_writer); mutex_unlock(&cpu_hotplug.lock); + cphp_lock_release(&cpu_hotplug.dep_map, 1, _RET_IP_); } EXPORT_SYMBOL_GPL(put_online_cpus); @@ -117,6 +133,7 @@ void cpu_hotplug_begin(void) { cpu_hotplug.active_writer = current; + cphp_lock_acquire(&cpu_hotplug.dep_map, 0, 0, _RET_IP_); for (;;) { mutex_lock(&cpu_hotplug.lock); if (likely(!cpu_hotplug.refcount)) @@ -131,6 +148,7 @@ void cpu_hotplug_done(void) { cpu_hotplug.active_writer = NULL; mutex_unlock(&cpu_hotplug.lock); + cphp_lock_release(&cpu_hotplug.dep_map, 1, _RET_IP_); } /* -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
