bcache: add separate workqueue for journal_write to avoid deadlock

goldhorn · axboe · commit 0f843e65d9ee · 2018-09-27T09:47:01.000-06:00
After write SSD completed, bcache schedules journal_write work to
system_wq, which is a public workqueue in system, without WQ_MEM_RECLAIM
flag. system_wq is also a bound wq, and there may be no idle kworker on
current processor. Creating a new kworker may unfortunately need to
reclaim memory first, by shrinking cache and slab used by vfs, which
depends on bcache device. That's a deadlock.

This patch create a new workqueue for journal_write with WQ_MEM_RECLAIM
flag. It's rescuer thread will work to avoid the deadlock.

Signed-off-by: Guoju Fang &lt;fangguoju@gmail.com&gt;
Cc: stable@vger.kernel.org
Signed-off-by: Coly Li &lt;colyli@suse.de&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
@@ -965,6 +965,7 @@ void bch_prio_write(struct cache *ca);
 void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent);
 
 extern struct workqueue_struct *bcache_wq;
+extern struct workqueue_struct *bch_journal_wq;
 extern struct mutex bch_register_lock;
 extern struct list_head bch_cache_sets;
 
diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
@@ -485,7 +485,7 @@ static void do_journal_discard(struct cache *ca)
 
 		closure_get(&ca->set->cl);
 		INIT_WORK(&ja->discard_work, journal_discard_work);
-		schedule_work(&ja->discard_work);
+		queue_work(bch_journal_wq, &ja->discard_work);
 	}
 }
 
@@ -592,7 +592,7 @@ static void journal_write_done(struct closure *cl)
 		: &j->w[0];
 
 	__closure_wake_up(&w->wait);
-	continue_at_nobarrier(cl, journal_write, system_wq);
+	continue_at_nobarrier(cl, journal_write, bch_journal_wq);
 }
 
 static void journal_write_unlock(struct closure *cl)
@@ -627,7 +627,7 @@ static void journal_write_unlocked(struct closure *cl)
 		spin_unlock(&c->journal.lock);
 
 		btree_flush_write(c);
-		continue_at(cl, journal_write, system_wq);
+		continue_at(cl, journal_write, bch_journal_wq);
 		return;
 	}
 
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
@@ -47,6 +47,7 @@ static int bcache_major;
 static DEFINE_IDA(bcache_device_idx);
 static wait_queue_head_t unregister_wait;
 struct workqueue_struct *bcache_wq;
+struct workqueue_struct *bch_journal_wq;
 
 #define BTREE_MAX_PAGES		(256 * 1024 / PAGE_SIZE)
 /* limitation of partitions number on single bcache device */
@@ -2341,6 +2342,9 @@ static void bcache_exit(void)
 		kobject_put(bcache_kobj);
 	if (bcache_wq)
 		destroy_workqueue(bcache_wq);
+	if (bch_journal_wq)
+		destroy_workqueue(bch_journal_wq);
+
 	if (bcache_major)
 		unregister_blkdev(bcache_major, "bcache");
 	unregister_reboot_notifier(&reboot);
@@ -2370,6 +2374,10 @@ static int __init bcache_init(void)
 	if (!bcache_wq)
 		goto err;
 
+	bch_journal_wq = alloc_workqueue("bch_journal", WQ_MEM_RECLAIM, 0);
+	if (!bch_journal_wq)
+		goto err;
+
 	bcache_kobj = kobject_create_and_add("bcache", fs_kobj);
 	if (!bcache_kobj)
 		goto err;

Original file line number	Diff line number	Diff line change
`@@ -485,7 +485,7 @@ static void do_journal_discard(struct cache *ca)`
`485`	`485`
`486`	`486`	`closure_get(&ca->set->cl);`
`487`	`487`	`INIT_WORK(&ja->discard_work, journal_discard_work);`
`488`		`- schedule_work(&ja->discard_work);`
	`488`	`+ queue_work(bch_journal_wq, &ja->discard_work);`
`489`	`489`	`}`
`490`	`490`	`}`
`491`	`491`
`@@ -592,7 +592,7 @@ static void journal_write_done(struct closure *cl)`
`592`	`592`	`: &j->w[0];`
`593`	`593`
`594`	`594`	`__closure_wake_up(&w->wait);`
`595`		`- continue_at_nobarrier(cl, journal_write, system_wq);`
	`595`	`+ continue_at_nobarrier(cl, journal_write, bch_journal_wq);`
`596`	`596`	`}`
`597`	`597`
`598`	`598`	`static void journal_write_unlock(struct closure *cl)`
`@@ -627,7 +627,7 @@ static void journal_write_unlocked(struct closure *cl)`
`627`	`627`	`spin_unlock(&c->journal.lock);`
`628`	`628`
`629`	`629`	`btree_flush_write(c);`
`630`		`- continue_at(cl, journal_write, system_wq);`
	`630`	`+ continue_at(cl, journal_write, bch_journal_wq);`
`631`	`631`	`return;`
`632`	`632`	`}`
`633`	`633`