bcache: Allocation kthread fixes

The alloc kthread should've been using try_to_freeze() - and also there
was the potential for the alloc kthread to get woken up after it had
shut down, which would have been bad.
Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/alloc.c

@@ -63,6 +63,7 @@
 #include "bcache.h"
 #include "btree.h"
 
+#include <linux/freezer.h>
 #include <linux/kthread.h>
 #include <linux/random.h>
 #include <trace/events/bcache.h>
@@ -363,11 +364,10 @@ do {									\
 			break;						\
 									\
 		mutex_unlock(&(ca)->set->bucket_lock);			\
-		if (test_bit(CACHE_SET_STOPPING_2, &ca->set->flags)) {	\
-			closure_put(&ca->set->cl);			\
+		if (kthread_should_stop())				\
 			return 0;					\
-		}							\
 									\
+		try_to_freeze();					\
 		schedule();						\
 		mutex_lock(&(ca)->set->bucket_lock);			\
 	}								\
@@ -547,14 +547,12 @@ int bch_bucket_alloc_set(struct cache_set *c, unsigned watermark,
 
 int bch_cache_allocator_start(struct cache *ca)
 {
-	ca->alloc_thread = kthread_create(bch_allocator_thread,
-					  ca, "bcache_allocator");
-	if (IS_ERR(ca->alloc_thread))
-		return PTR_ERR(ca->alloc_thread);
-
-	closure_get(&ca->set->cl);
-	wake_up_process(ca->alloc_thread);
+	struct task_struct *k = kthread_run(bch_allocator_thread,
+					    ca, "bcache_allocator");
+	if (IS_ERR(k))
+		return PTR_ERR(k);
 
+	ca->alloc_thread = k;
 	return 0;
 }
 

drivers/md/bcache/bcache.h

@@ -664,13 +664,9 @@ struct gc_stat {
  * CACHE_SET_STOPPING always gets set first when we're closing down a cache set;
  * we'll continue to run normally for awhile with CACHE_SET_STOPPING set (i.e.
  * flushing dirty data).
- *
- * CACHE_SET_STOPPING_2 gets set at the last phase, when it's time to shut down
- * the allocation thread.
  */
 #define CACHE_SET_UNREGISTERING		0
 #define	CACHE_SET_STOPPING		1
-#define	CACHE_SET_STOPPING_2		2
 
 struct cache_set {
 	struct closure		cl;

drivers/md/bcache/super.c

@@ -16,6 +16,7 @@
 #include <linux/buffer_head.h>
 #include <linux/debugfs.h>
 #include <linux/genhd.h>
+#include <linux/kthread.h>
 #include <linux/module.h>
 #include <linux/random.h>
 #include <linux/reboot.h>
@@ -1329,11 +1330,9 @@ static void cache_set_free(struct closure *cl)
 static void cache_set_flush(struct closure *cl)
 {
 	struct cache_set *c = container_of(cl, struct cache_set, caching);
+	struct cache *ca;
 	struct btree *b;
-
-	/* Shut down allocator threads */
-	set_bit(CACHE_SET_STOPPING_2, &c->flags);
-	wake_up_allocators(c);
+	unsigned i;
 
 	bch_cache_accounting_destroy(&c->accounting);
 
@@ -1348,6 +1347,10 @@ static void cache_set_flush(struct closure *cl)
 		if (btree_node_dirty(b))
 			bch_btree_node_write(b, NULL);
 
+	for_each_cache(ca, c, i)
+		if (ca->alloc_thread)
+			kthread_stop(ca->alloc_thread);
+
 	closure_return(cl);
 }