block: fix lockdep warning on io_context release put_io_context()

11a3122f6c "block: strip out locking optimization in put_io_context()"
removed ioc_lock depth lockdep annoation along with locking
optimization; however, while recursing from put_io_context() is no
longer possible, ioc_release_fn() may still end up putting the last
reference of another ioc through elevator, which wlil grab ioc->lock
triggering spurious (as the ioc is always different one) A-A deadlock
warning.

As this can only happen one time from ioc_release_fn(), using non-zero
subclass from ioc_release_fn() is enough.  Use subclass 1.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 14 insertions, 7 deletions

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 9884fd7427fe..8b782a63c297 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -80,8 +80,15 @@ static void ioc_release_fn(struct work_struct *work)
         struct io_context *ioc = container_of(work, struct io_context,
                                               release_work);
         struct request_queue *last_q = NULL;
+        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)) {
                 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
@@ -103,15 +110,15 @@ static void ioc_release_fn(struct work_struct *work)
                          */
                         if (last_q) {
                                 spin_unlock(last_q->queue_lock);
-                                spin_unlock_irq(&ioc->lock);
+                                spin_unlock_irqrestore(&ioc->lock, flags);
                                 blk_put_queue(last_q);
                         } else {
-                                spin_unlock_irq(&ioc->lock);
+                                spin_unlock_irqrestore(&ioc->lock, flags);
                         }
 
                         last_q = this_q;
-                        spin_lock_irq(this_q->queue_lock);
-                        spin_lock(&ioc->lock);
+                        spin_lock_irqsave(this_q->queue_lock, flags);
+                        spin_lock_nested(&ioc->lock, 1);
                         continue;
                 }
                 ioc_exit_icq(icq);
@@ -119,10 +126,10 @@ static void ioc_release_fn(struct work_struct *work)
 
         if (last_q) {
                 spin_unlock(last_q->queue_lock);
-                spin_unlock_irq(&ioc->lock);
+                spin_unlock_irqrestore(&ioc->lock, flags);
                 blk_put_queue(last_q);
         } else {
-                spin_unlock_irq(&ioc->lock);
+                spin_unlock_irqrestore(&ioc->lock, flags);
         }
 
         kmem_cache_free(iocontext_cachep, ioc);