[PATCH 1/2] block: remove unnecessary ioc nested locking
From: John Ogness <john.ogness@linutronix.de>
Date: 2020-06-19 15:20:51
Also in:
lkml
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
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 d8c66c5d5924 ("block: fix lockdep warning on io_context release
put_io_context()") by using a nested subclass for the ioc spinlock.
However, with commit f382fb0bcef4 ("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>
---
block/blk-ioc.c | 26 ++++++--------------------
1 file changed, 6 insertions(+), 20 deletions(-)
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 9df50fb507ca..5dbcfa1b872e 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c@@ -96,15 +96,7 @@ static void ioc_release_fn(struct work_struct *work) { struct io_context *ioc = container_of(work, struct io_context, release_work); - unsigned long flags; - - /* - * 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); + spin_lock_irq(&ioc->lock); while (!hlist_empty(&ioc->icq_list)) { 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); spin_unlock(&q->queue_lock); } else { - spin_unlock_irqrestore(&ioc->lock, flags); + spin_unlock_irq(&ioc->lock); 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); }
@@ -170,7 +162,6 @@ void put_io_context(struct io_context *ioc) */ void put_io_context_active(struct io_context *ioc) { - unsigned long flags; struct io_cq *icq; if (!atomic_dec_and_test(&ioc->active_ref)) {
@@ -178,19 +169,14 @@ void put_io_context_active(struct io_context *ioc) return; } - /* - * 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); + spin_lock_irq(&ioc->lock); hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) { if (icq->flags & ICQ_EXITED) continue; ioc_exit_icq(icq); } - spin_unlock_irqrestore(&ioc->lock, flags); + spin_unlock_irq(&ioc->lock); put_io_context(ioc); }
--
2.20.1