Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of callbackregistration functions

[Srivatsa S. Bhat]

On 02/10/2014 04:21 PM, Gautham R Shenoy wrote:
> On Mon, Feb 10, 2014 at 02:45:55PM +0530, Srivatsa S. Bhat wrote:
>> Hi Gautham,
>>
>> On 02/08/2014 12:41 AM, Gautham R Shenoy wrote:
>>> 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.
>>>>
[...]
>> This patch looks good to me. I have a couple of suggestions though..
>>
> 
> Thanks. I have incorporated the suggestions. Could you check if the
> following looks good ?
> 
> ---
>  Add lockdep annotations for get/put_online_cpus() and
>  cpu_hotplug_begin()/cpu_hotplug_end().
> 
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Cc: Srivatsa Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Gautham R. Shenoy <ego@xxxxxxxxxxxxxxxxxx>

Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>

Regards,
Srivatsa S. Bhat

> ---
>  kernel/cpu.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index deff2e6..33caf5e 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"
> 
> @@ -57,17 +58,30 @@ 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
>  };
> 
> +/* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
> +#define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
> +#define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)
> +#define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)
> +
>  void get_online_cpus(void)
>  {
>  	might_sleep();
>  	if (cpu_hotplug.active_writer == current)
>  		return;
> +	cpuhp_lock_acquire_read();
>  	mutex_lock(&cpu_hotplug.lock);
>  	cpu_hotplug.refcount++;
>  	mutex_unlock(&cpu_hotplug.lock);
> @@ -87,6 +101,7 @@ 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);
> +	cpuhp_lock_release();
> 
>  }
>  EXPORT_SYMBOL_GPL(put_online_cpus);
> @@ -117,6 +132,7 @@ void cpu_hotplug_begin(void)
>  {
>  	cpu_hotplug.active_writer = current;
> 
> +	cpuhp_lock_acquire();
>  	for (;;) {
>  		mutex_lock(&cpu_hotplug.lock);
>  		if (likely(!cpu_hotplug.refcount))
> @@ -131,6 +147,7 @@ void cpu_hotplug_done(void)
>  {
>  	cpu_hotplug.active_writer = NULL;
>  	mutex_unlock(&cpu_hotplug.lock);
> +	cpuhp_lock_release();
>  }
> 
>  /*
> 

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