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block, cfq: fix race condition in cic creation path and tighten locking 

cfq_get_io_context() would fail if multiple tasks race to insert cic's
for the same association.  This patch restructures
cfq_get_io_context() such that slow path insertion race is handled
properly.

Note that the restructuring also makes cfq_get_io_context() called
under queue_lock and performs both ioc and cfqd insertions while
holding both ioc and queue locks.  This is part of on-going locking
tightening and will be used to simplify synchronization rules.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo 2011-12-14 00:33:38 +01:00 committed by Jens Axboe
parent dc86900e0a
commit 216284c352
1 changed files with 74 additions and 57 deletions
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131
block/cfq-iosched.c
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@ -2908,13 +2908,10 @@ static void changed_ioprio(struct cfq_io_context *cic)
{
struct cfq_data *cfqd = cic_to_cfqd(cic);
struct cfq_queue *cfqq;
unsigned long flags;
if (unlikely(!cfqd))
return;
spin_lock_irqsave(cfqd->queue->queue_lock, flags);
cfqq = cic->cfqq[BLK_RW_ASYNC];
if (cfqq) {
struct cfq_queue *new_cfqq;
@ -2929,8 +2926,6 @@ static void changed_ioprio(struct cfq_io_context *cic)
cfqq = cic->cfqq[BLK_RW_SYNC];
if (cfqq)
cfq_mark_cfqq_prio_changed(cfqq);
spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}
static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
@ -2958,7 +2953,6 @@ static void changed_cgroup(struct cfq_io_context *cic)
{
struct cfq_queue *sync_cfqq = cic_to_cfqq(cic, 1);
struct cfq_data *cfqd = cic_to_cfqd(cic);
unsigned long flags;
struct request_queue *q;
if (unlikely(!cfqd))
@ -2966,8 +2960,6 @@ static void changed_cgroup(struct cfq_io_context *cic)
q = cfqd->queue;
spin_lock_irqsave(q->queue_lock, flags);
if (sync_cfqq) {
/*
* Drop reference to sync queue. A new sync queue will be
@ -2977,8 +2969,6 @@ static void changed_cgroup(struct cfq_io_context *cic)
cic_set_cfqq(cic, NULL, 1);
cfq_put_queue(sync_cfqq);
}
spin_unlock_irqrestore(q->queue_lock, flags);
}
#endif /* CONFIG_CFQ_GROUP_IOSCHED */
@ -3142,16 +3132,31 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
return cic;
}
/*
* Add cic into ioc, using cfqd as the search key. This enables us to lookup
* the process specific cfq io context when entered from the block layer.
* Also adds the cic to a per-cfqd list, used when this queue is removed.
/**
* cfq_create_cic - create and link a cfq_io_context
* @cfqd: cfqd of interest
* @gfp_mask: allocation mask
*
* Make sure cfq_io_context linking %current->io_context and @cfqd exists.
* If ioc and/or cic doesn't exist, they will be created using @gfp_mask.
*/
static int cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
struct cfq_io_context *cic, gfp_t gfp_mask)
static int cfq_create_cic(struct cfq_data *cfqd, gfp_t gfp_mask)
{
unsigned long flags;
int ret;
struct request_queue *q = cfqd->queue;
struct cfq_io_context *cic = NULL;
struct io_context *ioc;
int ret = -ENOMEM;
might_sleep_if(gfp_mask & __GFP_WAIT);
/* allocate stuff */
ioc = current_io_context(gfp_mask, q->node);
if (!ioc)
goto out;
cic = cfq_alloc_io_context(cfqd, gfp_mask);
if (!cic)
goto out;
ret = radix_tree_preload(gfp_mask);
if (ret)
@ -3161,53 +3166,72 @@ static int cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
cic->key = cfqd;
cic->q = cfqd->queue;
spin_lock_irqsave(&ioc->lock, flags);
ret = radix_tree_insert(&ioc->radix_root, cfqd->queue->id, cic);
if (!ret)
/* lock both q and ioc and try to link @cic */
spin_lock_irq(q->queue_lock);
spin_lock(&ioc->lock);
ret = radix_tree_insert(&ioc->radix_root, q->id, cic);
if (likely(!ret)) {
hlist_add_head_rcu(&cic->cic_list, &ioc->cic_list);
spin_unlock_irqrestore(&ioc->lock, flags);
list_add(&cic->queue_list, &cfqd->cic_list);
cic = NULL;
} else if (ret == -EEXIST) {
/* someone else already did it */
ret = 0;
}
spin_unlock(&ioc->lock);
spin_unlock_irq(q->queue_lock);
radix_tree_preload_end();
if (!ret) {
spin_lock_irqsave(cfqd->queue->queue_lock, flags);
list_add(&cic->queue_list, &cfqd->cic_list);
spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}
out:
if (ret)
printk(KERN_ERR "cfq: cic link failed!\n");
if (cic)
cfq_cic_free(cic);
return ret;
}
/*
* Setup general io context and cfq io context. There can be several cfq
* io contexts per general io context, if this process is doing io to more
* than one device managed by cfq.
/**
* cfq_get_io_context - acquire cfq_io_context and bump refcnt on io_context
* @cfqd: cfqd to setup cic for
* @gfp_mask: allocation mask
*
* Return cfq_io_context associating @cfqd and %current->io_context and
* bump refcnt on io_context. If ioc or cic doesn't exist, they're created
* using @gfp_mask.
*
* Must be called under queue_lock which may be released and re-acquired.
* This function also may sleep depending on @gfp_mask.
*/
static struct cfq_io_context *
cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
{
struct io_context *ioc = NULL;
struct request_queue *q = cfqd->queue;
struct cfq_io_context *cic = NULL;
struct io_context *ioc;
int err;
might_sleep_if(gfp_mask & __GFP_WAIT);
lockdep_assert_held(q->queue_lock);
ioc = current_io_context(gfp_mask, cfqd->queue->node);
if (!ioc)
goto err;
while (true) {
/* fast path */
ioc = current->io_context;
if (likely(ioc)) {
cic = cfq_cic_lookup(cfqd, ioc);
if (likely(cic))
break;
}
cic = cfq_cic_lookup(cfqd, ioc);
if (cic)
goto out;
/* slow path - unlock, create missing ones and retry */
spin_unlock_irq(q->queue_lock);
err = cfq_create_cic(cfqd, gfp_mask);
spin_lock_irq(q->queue_lock);
if (err)
return NULL;
}
cic = cfq_alloc_io_context(cfqd, gfp_mask);
if (cic == NULL)
goto err;
if (cfq_cic_link(cfqd, ioc, cic, gfp_mask))
goto err;
out:
/* bump @ioc's refcnt and handle changed notifications */
get_io_context(ioc);
if (unlikely(cic->changed)) {
@ -3220,10 +3244,6 @@ out:
}
return cic;
err:
if (cic)
cfq_cic_free(cic);
return NULL;
}
static void
@ -3759,14 +3779,11 @@ cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
const int rw = rq_data_dir(rq);
const bool is_sync = rq_is_sync(rq);
struct cfq_queue *cfqq;
unsigned long flags;
might_sleep_if(gfp_mask & __GFP_WAIT);
spin_lock_irq(q->queue_lock);
cic = cfq_get_io_context(cfqd, gfp_mask);
spin_lock_irqsave(q->queue_lock, flags);
if (!cic)
goto queue_fail;
@ -3802,12 +3819,12 @@ new_queue:
rq->elevator_private[0] = cic;
rq->elevator_private[1] = cfqq;
rq->elevator_private[2] = cfq_ref_get_cfqg(cfqq->cfqg);
spin_unlock_irqrestore(q->queue_lock, flags);
spin_unlock_irq(q->queue_lock);
return 0;
queue_fail:
cfq_schedule_dispatch(cfqd);
spin_unlock_irqrestore(q->queue_lock, flags);
spin_unlock_irq(q->queue_lock);
cfq_log(cfqd, "set_request fail");
return 1;
}