vmw_balloon: dynamically allocate the vmw-balloon shrinker

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the vmw-balloon shrinker, so that it can be freed
asynchronously via RCU. Then it doesn't need to wait for RCU read-side
critical section when releasing the struct vmballoon.

And we can simply exit vmballoon_init() when registering the shrinker
fails. So the shrinker_registered indication is redundant, just remove it.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Qi Zheng <[e-mail]>
Reviewed-by: Muchun Song <[e-mail]>
Acked-by: Nadav Amit <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Abhinav Kumar <[e-mail]>
Cc: Alasdair Kergon <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Alyssa Rosenzweig <[e-mail]>
Cc: Andreas Dilger <[e-mail]>
Cc: Andreas Gruenbacher <[e-mail]>
Cc: Anna Schumaker <[e-mail]>
Cc: Bob Peterson <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Carlos Llamas <[e-mail]>
Cc: Chandan Babu R <[e-mail]>
Cc: Chao Yu <[e-mail]>
Cc: Chris Mason <[e-mail]>
Cc: Christian Brauner <[e-mail]>
Cc: Christian Koenig <[e-mail]>
Cc: Chuck Lever <[e-mail]>
Cc: Coly Li <[e-mail]>
Cc: Dai Ngo <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: "Darrick J. Wong" <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: David Sterba <[e-mail]>
Cc: Dmitry Baryshkov <[e-mail]>
Cc: Gao Xiang <[e-mail]>
Cc: Huang Rui <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jaegeuk Kim <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Jason Wang <[e-mail]>
Cc: Jeff Layton <[e-mail]>
Cc: Jeffle Xu <[e-mail]>
Cc: Joel Fernandes (Google) <[e-mail]>
Cc: Joonas Lahtinen <[e-mail]>
Cc: Josef Bacik <[e-mail]>
Cc: Juergen Gross <[e-mail]>
Cc: Kent Overstreet <[e-mail]>
Cc: Kirill Tkhai <[e-mail]>
Cc: Marijn Suijten <[e-mail]>
Cc: "Michael S. Tsirkin" <[e-mail]>
Cc: Mike Snitzer <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Muchun Song <[e-mail]>
Cc: Neil Brown <[e-mail]>
Cc: Oleksandr Tyshchenko <[e-mail]>
Cc: Olga Kornievskaia <[e-mail]>
Cc: Paul E. McKenney <[e-mail]>
Cc: Richard Weinberger <[e-mail]>
Cc: Rob Clark <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Rodrigo Vivi <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Sean Paul <[e-mail]>
Cc: Sergey Senozhatsky <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: Stefano Stabellini <[e-mail]>
Cc: Steven Price <[e-mail]>
Cc: "Theodore Ts'o" <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Tomeu Vizoso <[e-mail]>
Cc: Tom Talpey <[e-mail]>
Cc: Trond Myklebust <[e-mail]>
Cc: Tvrtko Ursulin <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Xuan Zhuo <[e-mail]>
Cc: Yue Hu <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

drivers/misc/vmw_balloon.c

···
 	/**
 	 * @shrinker: shrinker interface that is used to avoid over-inflation.
 	 */
-	struct shrinker shrinker;
-
-	/**
-	 * @shrinker_registered: whether the shrinker was registered.
-	 *
-	 * The shrinker interface does not handle gracefully the removal of
-	 * shrinker that was not registered before. This indication allows to
-	 * simplify the unregistration process.
-	 */
-	bool shrinker_registered;
+	struct shrinker *shrinker;
 };
 
 static struct vmballoon balloon;
···
 
 static void vmballoon_unregister_shrinker(struct vmballoon *b)
 {
-	if (b->shrinker_registered)
-		unregister_shrinker(&b->shrinker);
-	b->shrinker_registered = false;
+	shrinker_free(b->shrinker);
+	b->shrinker = NULL;
 }
 
 static int vmballoon_register_shrinker(struct vmballoon *b)
 {
-	int r;
-
 	/* Do nothing if the shrinker is not enabled */
 	if (!vmwballoon_shrinker_enable)
 		return 0;
 
-	b->shrinker.scan_objects = vmballoon_shrinker_scan;
-	b->shrinker.count_objects = vmballoon_shrinker_count;
-	b->shrinker.seeks = DEFAULT_SEEKS;
+	b->shrinker = shrinker_alloc(0, "vmw-balloon");
+	if (!b->shrinker)
+		return -ENOMEM;
 
-	r = register_shrinker(&b->shrinker, "vmw-balloon");
+	b->shrinker->scan_objects = vmballoon_shrinker_scan;
+	b->shrinker->count_objects = vmballoon_shrinker_count;
+	b->shrinker->private_data = b;
 
-	if (r == 0)
-		b->shrinker_registered = true;
+	shrinker_register(b->shrinker);
 
-	return r;
+	return 0;
 }
 
 /*
···
 
 	error = vmballoon_register_shrinker(&balloon);
 	if (error)
-		goto fail;
+		return error;
 
 	/*
 	 * Initialization of compaction must be done after the call to
···
 	vmballoon_debugfs_init(&balloon);
 
 	return 0;
-fail:
-	vmballoon_unregister_shrinker(&balloon);
-	return error;
 }
 
 /*