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block: remove unnecessary ioc nested locking

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The legacy CFQ IO scheduler could call put_io_context() in its exit_icq()
elevator callback. This led to a lockdep warning, which was fixed in
commit d8c66c5d59 ("block: fix lockdep warning on io_context release
put_io_context()") by using a nested subclass for the ioc spinlock.
However, with commit f382fb0bce ("block: remove legacy IO schedulers")
the CFQ IO scheduler no longer exists.

The BFQ IO scheduler also implements the exit_icq() elevator callback but
does not call put_io_context().

The nested subclass for the ioc spinlock is no longer needed. Since it
existed as an exception and no longer applies, remove the nested subclass
usage.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
John Ogness
2020-06-19 17:23:17 +02:06
committed by Jens Axboe
parent 5b642d8b9f
commit a43f085f87
1 changed files with 6 additions and 20 deletions
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26
block/blk-ioc.c
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@@ -96,15 +96,7 @@ static void ioc_release_fn(struct work_struct *work)
{ {
struct io_context *ioc = container_of(work, struct io_context, struct io_context *ioc = container_of(work, struct io_context,
release_work); release_work);
unsigned long flags; spin_lock_irq(&ioc->lock);
/*
* Exiting icq may call into put_io_context() through elevator
* which will trigger lockdep warning. The ioc's are guaranteed to
* be different, use a different locking subclass here. Use
* irqsave variant as there's no spin_lock_irq_nested().
*/
spin_lock_irqsave_nested(&ioc->lock, flags, 1);
while (!hlist_empty(&ioc->icq_list)) { while (!hlist_empty(&ioc->icq_list)) {
struct io_cq *icq = hlist_entry(ioc->icq_list.first, struct io_cq *icq = hlist_entry(ioc->icq_list.first,
@@ -115,13 +107,13 @@ static void ioc_release_fn(struct work_struct *work)
ioc_destroy_icq(icq); ioc_destroy_icq(icq);
spin_unlock(&q->queue_lock); spin_unlock(&q->queue_lock);
} else { } else {
spin_unlock_irqrestore(&ioc->lock, flags); spin_unlock_irq(&ioc->lock);
cpu_relax(); cpu_relax();
spin_lock_irqsave_nested(&ioc->lock, flags, 1); spin_lock_irq(&ioc->lock);
} }
} }
spin_unlock_irqrestore(&ioc->lock, flags); spin_unlock_irq(&ioc->lock);
kmem_cache_free(iocontext_cachep, ioc); kmem_cache_free(iocontext_cachep, ioc);
} }
@@ -170,7 +162,6 @@ void put_io_context(struct io_context *ioc)
*/ */
void put_io_context_active(struct io_context *ioc) void put_io_context_active(struct io_context *ioc)
{ {
unsigned long flags;
struct io_cq *icq; struct io_cq *icq;
if (!atomic_dec_and_test(&ioc->active_ref)) { if (!atomic_dec_and_test(&ioc->active_ref)) {
@@ -178,19 +169,14 @@ void put_io_context_active(struct io_context *ioc)
return; return;
} }
/* spin_lock_irq(&ioc->lock);
* Need ioc lock to walk icq_list and q lock to exit icq. Perform
* reverse double locking. Read comment in ioc_release_fn() for
* explanation on the nested locking annotation.
*/
spin_lock_irqsave_nested(&ioc->lock, flags, 1);
hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) { hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
if (icq->flags & ICQ_EXITED) if (icq->flags & ICQ_EXITED)
continue; continue;
ioc_exit_icq(icq); ioc_exit_icq(icq);
} }
spin_unlock_irqrestore(&ioc->lock, flags); spin_unlock_irq(&ioc->lock);
put_io_context(ioc); put_io_context(ioc);
} }