Hi, Tejun, Forgot to send a pull-request? Add CC Linus.
Thanks, Lai On 09/03/13 07:15, Tejun Heo wrote: > From: Lai Jiangshan <la...@cn.fujitsu.com> > > Since multiple pools per cpu have been introduced, wq_unbind_fn() has > a subtle bug which may theoretically stall work item processing. The > problem is two-fold. > > * wq_unbind_fn() depends on the worker executing wq_unbind_fn() itself > to start unbound chain execution, which works fine when there was > only single pool. With multiple pools, only the pool which is > running wq_unbind_fn() - the highpri one - is guaranteed to have > such kick-off. The other pool could stall when its busy workers > block. > > * The current code is setting WORKER_UNBIND / POOL_DISASSOCIATED of > the two pools in succession without initiating work execution > inbetween. Because setting the flags requires grabbing assoc_mutex > which is held while new workers are created, this could lead to > stalls if a pool's manager is waiting for the previous pool's work > items to release memory. This is almost purely theoretical tho. > > Update wq_unbind_fn() such that it sets WORKER_UNBIND / > POOL_DISASSOCIATED, goes over schedule() and explicitly kicks off > execution for a pool and then moves on to the next one. > > tj: Updated comments and description. > > Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com> > Signed-off-by: Tejun Heo <t...@kernel.org> > Cc: sta...@vger.kernel.org > --- > As you seemingly has disappeared, I just fixed up this patch and > applied it to wq/for-3.9-fixes. > > Thanks. > > kernel/workqueue.c | 44 +++++++++++++++++++++++++------------------- > 1 file changed, 25 insertions(+), 19 deletions(-) > > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -3446,28 +3446,34 @@ static void wq_unbind_fn(struct work_str > > spin_unlock_irq(&pool->lock); > mutex_unlock(&pool->assoc_mutex); > - } > > - /* > - * Call schedule() so that we cross rq->lock and thus can guarantee > - * sched callbacks see the %WORKER_UNBOUND flag. This is necessary > - * as scheduler callbacks may be invoked from other cpus. > - */ > - schedule(); > + /* > + * Call schedule() so that we cross rq->lock and thus can > + * guarantee sched callbacks see the %WORKER_UNBOUND flag. > + * This is necessary as scheduler callbacks may be invoked > + * from other cpus. > + */ > + schedule(); > > - /* > - * Sched callbacks are disabled now. Zap nr_running. After this, > - * nr_running stays zero and need_more_worker() and keep_working() > - * are always true as long as the worklist is not empty. Pools on > - * @cpu now behave as unbound (in terms of concurrency management) > - * pools which are served by workers tied to the CPU. > - * > - * On return from this function, the current worker would trigger > - * unbound chain execution of pending work items if other workers > - * didn't already. > - */ > - for_each_std_worker_pool(pool, cpu) > + /* > + * Sched callbacks are disabled now. Zap nr_running. > + * After this, nr_running stays zero and need_more_worker() > + * and keep_working() are always true as long as the > + * worklist is not empty. This pool now behaves as an > + * unbound (in terms of concurrency management) pool which > + * are served by workers tied to the pool. > + */ > atomic_set(&pool->nr_running, 0); > + > + /* > + * With concurrency management just turned off, a busy > + * worker blocking could lead to lengthy stalls. Kick off > + * unbound chain execution of currently pending work items. > + */ > + spin_lock_irq(&pool->lock); > + wake_up_worker(pool); > + spin_unlock_irq(&pool->lock); > + } > } > > /* > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
