From ebd780ac233884d6ad298e29ba13d002da2ee5be Mon Sep 17 00:00:00 2001

From: Hannes Reinecke <hare@suse.de>

Date: Fri, 14 May 2021 12:44:38 +0200

Subject: [PATCH] block/genhd: use atomic_t for disk_event->block

References: bsc#1185497

Patch-Mainline: submitted linux-block 2021/06/01

__disk_unblock_events() will call queue_delayed_work() with a '0' argument

under a spin lock. This might cause the queue_work item to be executed

immediately, and run into a deadlock in disk_check_events() waiting for

the lock to be released.

This patch converts the 'blocked' counter into an atomic variable, so we don't

need to hold a spinlock anymore when scheduling the workqueue function.

Signed-off-by: Hannes Reinecke <hare@suse.de>

---

 block/genhd.c | 36 +++++++++++++-----------------------

 1 file changed, 13 insertions(+), 23 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c

index ab29d1a723b2..e1c3b9d2b5d6 100644

--- a/block/genhd.c

+++ b/block/genhd.c

@@ -1731,7 +1731,7 @@ struct disk_events {

 	spinlock_t		lock;

 	struct mutex		block_mutex;	/* protects blocking */

-	int			block;		/* event blocking depth */

+	atomic_t		block;		/* event blocking depth */

 	unsigned int		pending;	/* events already sent out */

 	unsigned int		clearing;	/* events being cleared */

@@ -1791,8 +1791,6 @@ static unsigned long disk_events_poll_jiffies(struct gendisk *disk)

 void disk_block_events(struct gendisk *disk)

 {

 	struct disk_events *ev = disk->ev;

-	unsigned long flags;

-	bool cancel;

 	if (!ev)

 		return;

@@ -1803,11 +1801,7 @@ void disk_block_events(struct gendisk *disk)

 	 */

 	mutex_lock(&ev->block_mutex);

-	spin_lock_irqsave(&ev->lock, flags);

-	cancel = !ev->block++;

-	spin_unlock_irqrestore(&ev->lock, flags);

-

-	if (cancel)

+	if (atomic_inc_return(&ev->block) == 1)

 		cancel_delayed_work_sync(&disk->ev->dwork);

 	mutex_unlock(&ev->block_mutex);

@@ -1819,23 +1813,19 @@ static void __disk_unblock_events(struct gendisk *disk, bool check_now)

 	unsigned long intv;

 	unsigned long flags;

+	if (atomic_dec_return(&ev->block) <= 0) {

+		mutex_unlock(&ev->block_mutex);

+		return;

+	}

 	spin_lock_irqsave(&ev->lock, flags);

-

-	if (WARN_ON_ONCE(ev->block <= 0))

-		goto out_unlock;

-

-	if (--ev->block)

-		goto out_unlock;

-

 	intv = disk_events_poll_jiffies(disk);

+	spin_unlock_irqrestore(&ev->lock, flags);

 	if (check_now)

 		queue_delayed_work(system_freezable_power_efficient_wq,

 				&ev->dwork, 0);

 	else if (intv)

 		queue_delayed_work(system_freezable_power_efficient_wq,

 				&ev->dwork, intv);

-out_unlock:

-	spin_unlock_irqrestore(&ev->lock, flags);

 }

 /**

@@ -1875,10 +1865,10 @@ void disk_flush_events(struct gendisk *disk, unsigned int mask)

 	spin_lock_irq(&ev->lock);

 	ev->clearing |= mask;

-	if (!ev->block)

+	spin_unlock_irq(&ev->lock);

+	if (!atomic_read(&ev->block))

 		mod_delayed_work(system_freezable_power_efficient_wq,

 				&ev->dwork, 0);

-	spin_unlock_irq(&ev->lock);

 }

 /**

@@ -1969,11 +1959,11 @@ static void disk_check_events(struct disk_events *ev,

 	*clearing_ptr &= ~clearing;

 	intv = disk_events_poll_jiffies(disk);

-	if (!ev->block && intv)

+	spin_unlock_irq(&ev->lock);

+	if (!atomic_read(&ev->block) && intv)

 		queue_delayed_work(system_freezable_power_efficient_wq,

 				&ev->dwork, intv);

-	spin_unlock_irq(&ev->lock);

 	/*

 	 * Tell userland about new events.  Only the events listed in

@@ -2138,7 +2128,7 @@ static void disk_alloc_events(struct gendisk *disk)

 	ev->disk = disk;

 	spin_lock_init(&ev->lock);

 	mutex_init(&ev->block_mutex);

-	ev->block = 1;

+	atomic_set(&ev->block, 1);

 	ev->poll_msecs = -1;

 	INIT_DELAYED_WORK(&ev->dwork, disk_events_workfn);

@@ -2182,6 +2172,6 @@ static void disk_del_events(struct gendisk *disk)

 static void disk_release_events(struct gendisk *disk)

 {

 	/* the block count should be 1 from disk_del_events() */

-	WARN_ON_ONCE(disk->ev && disk->ev->block != 1);

+	WARN_ON_ONCE(disk->ev && atomic_read(&disk->ev->block) != 1);

 	kfree(disk->ev);

 }

-- 

2.29.2