afs: Fix uninitialised spinlock afs_volume::cb_break_lock

Fix the cb_break_lock spinlock in afs_volume struct by initialising it when
the volume record is allocated.

Also rename the lock to cb_v_break_lock to distinguish it from the lock of
the same name in the afs_server struct.

Without this, the following trace may be observed when a volume-break
callback is received:

INFO: trying to register non-static key.
the code is fine but needs lockdep annotation.
turning off the locking correctness validator.
CPU: 2 PID: 50 Comm: kworker/2:1 Not tainted 5.2.0-rc1-fscache+ #3045
Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
Workqueue: afs SRXAFSCB_CallBack
Call Trace:
dump_stack+0x67/0x8e
register_lock_class+0x23b/0x421
? check_usage_forwards+0x13c/0x13c
__lock_acquire+0x89/0xf73
lock_acquire+0x13b/0x166
? afs_break_callbacks+0x1b2/0x3dd
_raw_write_lock+0x2c/0x36
? afs_break_callbacks+0x1b2/0x3dd
afs_break_callbacks+0x1b2/0x3dd
? trace_event_raw_event_afs_server+0x61/0xac
SRXAFSCB_CallBack+0x11f/0x16c
process_one_work+0x2c5/0x4ee
? worker_thread+0x234/0x2ac
worker_thread+0x1d8/0x2ac
? cancel_delayed_work_sync+0xf/0xf
kthread+0x11f/0x127
? kthread_park+0x76/0x76
ret_from_fork+0x24/0x30

Fixes: 68251f0a6818 ("afs: Fix whole-volume callback handling")
Signed-off-by: David Howells <[e-mail]>

fs/afs/callback.c

···
 			struct afs_super_info *as = AFS_FS_S(cbi->sb);
 			struct afs_volume *volume = as->volume;
 
-			write_lock(&volume->cb_break_lock);
+			write_lock(&volume->cb_v_break_lock);
 			volume->cb_v_break++;
-			write_unlock(&volume->cb_break_lock);
+			write_unlock(&volume->cb_v_break_lock);
 		} else {
 			data.volume = NULL;
 			data.fid = *fid;

fs/afs/internal.h

···
 	unsigned int		servers_seq;	/* Incremented each time ->servers changes */
 
 	unsigned		cb_v_break;	/* Break-everything counter. */
-	rwlock_t		cb_break_lock;
+	rwlock_t		cb_v_break_lock;
 
 	afs_voltype_t		type;		/* type of volume */
 	short			error;

fs/afs/volume.c

···
 	atomic_set(&volume->usage, 1);
 	INIT_LIST_HEAD(&volume->proc_link);
 	rwlock_init(&volume->servers_lock);
+	rwlock_init(&volume->cb_v_break_lock);
 	memcpy(volume->name, vldb->name, vldb->name_len + 1);
 
 	slist = afs_alloc_server_list(params->cell, params->key, vldb, type_mask);