[linux-yocto] [PATCH 1/7] workqueue: use manager lock only to protect worker_idr

[Zumeng Chen]

On 2015年01月06日 06:28, Paul Gortmaker wrote:
> On 14-12-19 03:43 AM, Zumeng Chen wrote:
>> From: Lai Jiangshan <laijs at cn.fujitsu.com>
>>
>> worker_idr is highly bound to managers and is always/only accessed in manager
>> lock context. So we don't need pool->lock for it.
>>
>> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
>> Signed-off-by: Tejun Heo <tj at kernel.org>
>> (cherry picked from commit 9625ab1727743f6a164df26b7b1eeeced7380b42)
>> ---
> Even though "git cherry-pick -x <ID>" puts the upstream commit ID
> in the place shown here, I think you should get in the habit of
> what is done universally elsewhere for nearly all kernel patches,
> and put:
>
>    commit 9625ab1727743f6a164df26b7b1eeeced7380b42 upstream.
>
> as the 1st line of the long log.  Then the fact that it is already
> upstream is immediately obvious and not buried in a sea of SOB
> lines.  Which I note, your SOB line seems to be missing from all
> the ones I briefly looked at as well, so that should be fixed too.

OK, thanks Paul. I'll do it if these patches are still no in our tree :)

Cheers,
Zumeng

>
> Paul.
> --
>
>>   kernel/workqueue.c |   34 ++++++----------------------------
>>   1 file changed, 6 insertions(+), 28 deletions(-)
>>
>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>> index b4defde..701f2d2 100644
>> --- a/kernel/workqueue.c
>> +++ b/kernel/workqueue.c
>> @@ -124,8 +124,7 @@ enum {
>>    *    cpu or grabbing pool->lock is enough for read access.  If
>>    *    POOL_DISASSOCIATED is set, it's identical to L.
>>    *
>> - * MG: pool->manager_mutex and pool->lock protected.  Writes require both
>> - *     locks.  Reads can happen under either lock.
>> + * M: pool->manager_mutex protected.
>>    *
>>    * PL: wq_pool_mutex protected.
>>    *
>> @@ -164,7 +163,7 @@ struct worker_pool {
>>   	/* see manage_workers() for details on the two manager mutexes */
>>   	struct mutex		manager_arb;	/* manager arbitration */
>>   	struct mutex		manager_mutex;	/* manager exclusion */
>> -	struct idr		worker_idr;	/* MG: worker IDs and iteration */
>> +	struct idr		worker_idr;	/* M: worker IDs and iteration */
>>   
>>   	struct workqueue_attrs	*attrs;		/* I: worker attributes */
>>   	struct hlist_node	hash_node;	/* PL: unbound_pool_hash node */
>> @@ -340,16 +339,6 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
>>   			   lockdep_is_held(&wq->mutex),			\
>>   			   "sched RCU or wq->mutex should be held")
>>   
>> -#ifdef CONFIG_LOCKDEP
>> -#define assert_manager_or_pool_lock(pool)				\
>> -	WARN_ONCE(debug_locks &&					\
>> -		  !lockdep_is_held(&(pool)->manager_mutex) &&		\
>> -		  !lockdep_is_held(&(pool)->lock),			\
>> -		  "pool->manager_mutex or ->lock should be held")
>> -#else
>> -#define assert_manager_or_pool_lock(pool)	do { } while (0)
>> -#endif
>> -
>>   #define for_each_cpu_worker_pool(pool, cpu)				\
>>   	for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0];		\
>>   	     (pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
>> @@ -378,14 +367,14 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
>>    * @wi: integer used for iteration
>>    * @pool: worker_pool to iterate workers of
>>    *
>> - * This must be called with either @pool->manager_mutex or ->lock held.
>> + * This must be called with @pool->manager_mutex.
>>    *
>>    * The if/else clause exists only for the lockdep assertion and can be
>>    * ignored.
>>    */
>>   #define for_each_pool_worker(worker, wi, pool)				\
>>   	idr_for_each_entry(&(pool)->worker_idr, (worker), (wi))		\
>> -		if (({ assert_manager_or_pool_lock((pool)); false; })) { } \
>> +		if (({ lockdep_assert_held(&pool->manager_mutex); false; })) { } \
>>   		else
>>   
>>   /**
>> @@ -1718,13 +1707,7 @@ static struct worker *create_worker(struct worker_pool *pool)
>>   	 * ID is needed to determine kthread name.  Allocate ID first
>>   	 * without installing the pointer.
>>   	 */
>> -	idr_preload(GFP_KERNEL);
>> -	spin_lock_irq(&pool->lock);
>> -
>> -	id = idr_alloc(&pool->worker_idr, NULL, 0, 0, GFP_NOWAIT);
>> -
>> -	spin_unlock_irq(&pool->lock);
>> -	idr_preload_end();
>> +	id = idr_alloc(&pool->worker_idr, NULL, 0, 0, GFP_KERNEL);
>>   	if (id < 0)
>>   		goto fail;
>>   
>> @@ -1766,18 +1749,13 @@ static struct worker *create_worker(struct worker_pool *pool)
>>   		worker->flags |= WORKER_UNBOUND;
>>   
>>   	/* successful, commit the pointer to idr */
>> -	spin_lock_irq(&pool->lock);
>>   	idr_replace(&pool->worker_idr, worker, worker->id);
>> -	spin_unlock_irq(&pool->lock);
>>   
>>   	return worker;
>>   
>>   fail:
>> -	if (id >= 0) {
>> -		spin_lock_irq(&pool->lock);
>> +	if (id >= 0)
>>   		idr_remove(&pool->worker_idr, id);
>> -		spin_unlock_irq(&pool->lock);
>> -	}
>>   	kfree(worker);
>>   	return NULL;
>>   }
>>