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authorSteffen Klassert <steffen.klassert@secunet.com>2012-03-09 07:20:49 +0100
committerHerbert Xu <herbert@gondor.apana.org.au>2012-03-14 17:25:56 +0800
commit2dc9b5dbdef09840de852a4f0cc6a9c9eece7220 (patch)
tree4164272ddddfc2477005866ce3261c76470c0d1a /kernel
parent3047817b894ddae62be07787bc8735a616104398 (diff)
downloadop-kernel-dev-2dc9b5dbdef09840de852a4f0cc6a9c9eece7220.zip
op-kernel-dev-2dc9b5dbdef09840de852a4f0cc6a9c9eece7220.tar.gz
padata: Fix race on sequence number wrap
When padata_do_parallel() is called from multiple cpus for the same padata instance, we can get object reordering on sequence number wrap because testing for sequence number wrap and reseting the sequence number must happen atomically but is implemented with two atomic operations. This patch fixes this by converting the sequence number from atomic_t to an unsigned int and protect the access with a spin_lock. As a side effect, we get rid of the sequence number wrap handling because the seqence number wraps back to null now without the need to do anything. Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/padata.c38
1 files changed, 10 insertions, 28 deletions
diff --git a/kernel/padata.c b/kernel/padata.c
index aa99295..6f10eb2 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -29,7 +29,6 @@
#include <linux/sysfs.h>
#include <linux/rcupdate.h>
-#define MAX_SEQ_NR (INT_MAX - NR_CPUS)
#define MAX_OBJ_NUM 1000
static int padata_index_to_cpu(struct parallel_data *pd, int cpu_index)
@@ -43,18 +42,19 @@ static int padata_index_to_cpu(struct parallel_data *pd, int cpu_index)
return target_cpu;
}
-static int padata_cpu_hash(struct padata_priv *padata)
+static int padata_cpu_hash(struct parallel_data *pd)
{
int cpu_index;
- struct parallel_data *pd;
-
- pd = padata->pd;
/*
* Hash the sequence numbers to the cpus by taking
* seq_nr mod. number of cpus in use.
*/
- cpu_index = padata->seq_nr % cpumask_weight(pd->cpumask.pcpu);
+
+ spin_lock(&pd->seq_lock);
+ cpu_index = pd->seq_nr % cpumask_weight(pd->cpumask.pcpu);
+ pd->seq_nr++;
+ spin_unlock(&pd->seq_lock);
return padata_index_to_cpu(pd, cpu_index);
}
@@ -132,12 +132,7 @@ int padata_do_parallel(struct padata_instance *pinst,
padata->pd = pd;
padata->cb_cpu = cb_cpu;
- if (unlikely(atomic_read(&pd->seq_nr) == pd->max_seq_nr))
- atomic_set(&pd->seq_nr, -1);
-
- padata->seq_nr = atomic_inc_return(&pd->seq_nr);
-
- target_cpu = padata_cpu_hash(padata);
+ target_cpu = padata_cpu_hash(pd);
queue = per_cpu_ptr(pd->pqueue, target_cpu);
spin_lock(&queue->parallel.lock);
@@ -173,7 +168,7 @@ EXPORT_SYMBOL(padata_do_parallel);
static struct padata_priv *padata_get_next(struct parallel_data *pd)
{
int cpu, num_cpus;
- int next_nr, next_index;
+ unsigned int next_nr, next_index;
struct padata_parallel_queue *queue, *next_queue;
struct padata_priv *padata;
struct padata_list *reorder;
@@ -189,14 +184,6 @@ static struct padata_priv *padata_get_next(struct parallel_data *pd)
cpu = padata_index_to_cpu(pd, next_index);
next_queue = per_cpu_ptr(pd->pqueue, cpu);
- if (unlikely(next_nr > pd->max_seq_nr)) {
- next_nr = next_nr - pd->max_seq_nr - 1;
- next_index = next_nr % num_cpus;
- cpu = padata_index_to_cpu(pd, next_index);
- next_queue = per_cpu_ptr(pd->pqueue, cpu);
- pd->processed = 0;
- }
-
padata = NULL;
reorder = &next_queue->reorder;
@@ -205,8 +192,6 @@ static struct padata_priv *padata_get_next(struct parallel_data *pd)
padata = list_entry(reorder->list.next,
struct padata_priv, list);
- BUG_ON(next_nr != padata->seq_nr);
-
spin_lock(&reorder->lock);
list_del_init(&padata->list);
atomic_dec(&pd->reorder_objects);
@@ -402,7 +387,7 @@ static void padata_init_squeues(struct parallel_data *pd)
/* Initialize all percpu queues used by parallel workers */
static void padata_init_pqueues(struct parallel_data *pd)
{
- int cpu_index, num_cpus, cpu;
+ int cpu_index, cpu;
struct padata_parallel_queue *pqueue;
cpu_index = 0;
@@ -417,9 +402,6 @@ static void padata_init_pqueues(struct parallel_data *pd)
INIT_WORK(&pqueue->work, padata_parallel_worker);
atomic_set(&pqueue->num_obj, 0);
}
-
- num_cpus = cpumask_weight(pd->cpumask.pcpu);
- pd->max_seq_nr = num_cpus ? (MAX_SEQ_NR / num_cpus) * num_cpus - 1 : 0;
}
/* Allocate and initialize the internal cpumask dependend resources. */
@@ -446,7 +428,7 @@ static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst,
padata_init_pqueues(pd);
padata_init_squeues(pd);
setup_timer(&pd->timer, padata_reorder_timer, (unsigned long)pd);
- atomic_set(&pd->seq_nr, -1);
+ pd->seq_nr = 0;
atomic_set(&pd->reorder_objects, 0);
atomic_set(&pd->refcnt, 0);
pd->pinst = pinst;
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