From d46a5ac7a7e2045e33c6ad6ffb8cf18a7e86a15a Mon Sep 17 00:00:00 2001 From: Steffen Klassert Date: Wed, 19 May 2010 13:43:14 +1000 Subject: [PATCH] padata: Use a timer to handle remaining objects in the reorder queues padata_get_next needs to check whether the next object that need serialization must be parallel processed by the local cpu. This check was wrong implemented and returned always true, so the try_again loop in padata_reorder was never taken. This can lead to object leaks in some rare cases due to a race that appears with the trylock in padata_reorder. The try_again loop was not a good idea after all, because a cpu could take that loop frequently, so we handle this with a timer instead. This patch adds a timer to handle the race that appears with the trylock. If cpu1 queues an object to the reorder queue while cpu2 holds the pd->lock but left the while loop in padata_reorder already, cpu2 can't care for this object and cpu1 exits because it can't get the lock. Usually the next cpu that takes the lock cares for this object too. We need the timer just if this object was the last one that arrives to the reorder queues. The timer function sends it out in this case. Signed-off-by: Steffen Klassert Signed-off-by: Herbert Xu --- include/linux/padata.h | 2 ++ kernel/padata.c | 25 ++++++++++++++++++------- 2 files changed, 20 insertions(+), 7 deletions(-) diff --git a/include/linux/padata.h b/include/linux/padata.h index 51611da9c498..64836a63bd17 100644 --- a/include/linux/padata.h +++ b/include/linux/padata.h @@ -24,6 +24,7 @@ #include #include #include +#include struct padata_priv { struct list_head list; @@ -60,6 +61,7 @@ struct parallel_data { unsigned int max_seq_nr; cpumask_var_t cpumask; spinlock_t lock; + struct timer_list timer; }; struct padata_instance { diff --git a/kernel/padata.c b/kernel/padata.c index 82958e01564b..6d7ea481b716 100644 --- a/kernel/padata.c +++ b/kernel/padata.c @@ -231,7 +231,8 @@ static struct padata_priv *padata_get_next(struct parallel_data *pd) goto out; } - if (next_nr % num_cpus == next_queue->cpu_index) { + queue = per_cpu_ptr(pd->queue, smp_processor_id()); + if (queue->cpu_index == next_queue->cpu_index) { padata = ERR_PTR(-ENODATA); goto out; } @@ -247,9 +248,8 @@ static void padata_reorder(struct parallel_data *pd) struct padata_queue *queue; struct padata_instance *pinst = pd->pinst; -try_again: if (!spin_trylock_bh(&pd->lock)) - goto out; + return; while (1) { padata = padata_get_next(pd); @@ -258,8 +258,9 @@ try_again: break; if (PTR_ERR(padata) == -ENODATA) { + del_timer(&pd->timer); spin_unlock_bh(&pd->lock); - goto out; + return; } queue = per_cpu_ptr(pd->queue, padata->cb_cpu); @@ -273,13 +274,22 @@ try_again: spin_unlock_bh(&pd->lock); - if (atomic_read(&pd->reorder_objects)) - goto try_again; + if (atomic_read(&pd->reorder_objects) + && !(pinst->flags & PADATA_RESET)) + mod_timer(&pd->timer, jiffies + HZ); + else + del_timer(&pd->timer); -out: return; } +static void padata_reorder_timer(unsigned long arg) +{ + struct parallel_data *pd = (struct parallel_data *)arg; + + padata_reorder(pd); +} + static void padata_serial_worker(struct work_struct *work) { struct padata_queue *queue; @@ -383,6 +393,7 @@ static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst, num_cpus = cpumask_weight(pd->cpumask); pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1; + setup_timer(&pd->timer, padata_reorder_timer, (unsigned long)pd); atomic_set(&pd->seq_nr, -1); atomic_set(&pd->reorder_objects, 0); atomic_set(&pd->refcnt, 0); -- 2.20.1