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Subject[PATCH block/for-linus 2/3] block: simplify ioc_release_fn()
Reverse double lock dancing in ioc_release_fn() can be simplified by
just using trylock on the queue_lock and back out from ioc lock on
trylock failure. Simplify it.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
block/blk-ioc.c | 44 +++++++++-----------------------------------
1 file changed, 9 insertions(+), 35 deletions(-)

Index: work/block/blk-ioc.c
===================================================================
--- work.orig/block/blk-ioc.c
+++ work/block/blk-ioc.c
@@ -79,7 +79,6 @@ static void ioc_release_fn(struct work_s
{
struct io_context *ioc = container_of(work, struct io_context,
release_work);
- struct request_queue *last_q = NULL;
unsigned long flags;

/*
@@ -93,44 +92,19 @@ static void ioc_release_fn(struct work_s
while (!hlist_empty(&ioc->icq_list)) {
struct io_cq *icq = hlist_entry(ioc->icq_list.first,
struct io_cq, ioc_node);
- struct request_queue *this_q = icq->q;
+ struct request_queue *q = icq->q;

- if (this_q != last_q) {
- /*
- * Need to switch to @this_q. Once we release
- * @ioc->lock, it can go away along with @cic.
- * Hold on to it.
- */
- __blk_get_queue(this_q);
-
- /*
- * blk_put_queue() might sleep thanks to kobject
- * idiocy. Always release both locks, put and
- * restart.
- */
- if (last_q) {
- spin_unlock(last_q->queue_lock);
- spin_unlock_irqrestore(&ioc->lock, flags);
- blk_put_queue(last_q);
- } else {
- spin_unlock_irqrestore(&ioc->lock, flags);
- }
-
- last_q = this_q;
- spin_lock_irqsave(this_q->queue_lock, flags);
- spin_lock_nested(&ioc->lock, 1);
- continue;
+ if (spin_trylock(q->queue_lock)) {
+ ioc_exit_icq(icq);
+ spin_unlock(q->queue_lock);
+ } else {
+ spin_unlock_irqrestore(&ioc->lock, flags);
+ cpu_relax();
+ spin_lock_irqsave_nested(&ioc->lock, flags, 1);
}
- ioc_exit_icq(icq);
}

- if (last_q) {
- spin_unlock(last_q->queue_lock);
- spin_unlock_irqrestore(&ioc->lock, flags);
- blk_put_queue(last_q);
- } else {
- spin_unlock_irqrestore(&ioc->lock, flags);
- }
+ spin_unlock_irqrestore(&ioc->lock, flags);

kmem_cache_free(iocontext_cachep, ioc);
}

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