Hello,
This series removes a retry loop in the ioc reverse-order
double lock dance, replacing it with an implementation that
uses guaranteed forward progress.
While at it, it also removes the nested spinlock usage,
which no longer applies since CFQ is gone.
John Ogness (2):
block: remove unnecessary ioc nested locking
block: remove retry loop in ioc_release_fn()
block/blk-ioc.c | 42 +++++++++++++++++++++---------------------
1 file changed, 21 insertions(+), 21 deletions(-)
--
2.20.1
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 <[email protected]>
---
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
On Fri, Jun 19, 2020 at 05:23:17PM +0206, John Ogness wrote:
> 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 <[email protected]>
As far I can tell, looks good.
Reviewed-by: Daniel Wagner <[email protected]>
On 6/19/20 9:17 AM, John Ogness wrote:
> Hello,
>
> This series removes a retry loop in the ioc reverse-order
> double lock dance, replacing it with an implementation that
> uses guaranteed forward progress.
>
> While at it, it also removes the nested spinlock usage,
> which no longer applies since CFQ is gone.
Applied for 5.9, thanks.
--
Jens Axboe