lib: atomic64: Initialize locks statically to fix early users

The atomic64 library uses a handful of static spin locks to implement
atomic 64-bit operations on architectures without support for atomic
64-bit instructions.

Unfortunately, the spinlocks are initialized in a pure initcall and that
is too late for the vfs namespace code which wants to use atomic64
operations before the initcall is run.

This became a problem as of commit 8823c079ba71: "vfs: Add setns support
for the mount namespace".

This leads to BUG messages such as:

BUG: spinlock bad magic on CPU#0, swapper/0/0
lock: atomic64_lock+0x240/0x400, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
do_raw_spin_lock+0x158/0x198
_raw_spin_lock_irqsave+0x4c/0x58
atomic64_add_return+0x30/0x5c
alloc_mnt_ns.clone.14+0x44/0xac
create_mnt_ns+0xc/0x54
mnt_init+0x120/0x1d4
vfs_caches_init+0xe0/0x10c
start_kernel+0x29c/0x300

coming out early on during boot when spinlock debugging is enabled.

Fix this by initializing the spinlocks statically at compile time.

Reported-and-tested-by: Vaibhav Bedia <[e-mail]>
Tested-by: Tony Lindgren <[e-mail]>
Cc: Eric W. Biederman <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/atomic64.c

···
 static union {
 	raw_spinlock_t lock;
 	char pad[L1_CACHE_BYTES];
-} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp;
+} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp = {
+	[0 ... (NR_LOCKS - 1)] = {
+		.lock =  __RAW_SPIN_LOCK_UNLOCKED(atomic64_lock.lock),
+	},
+};
 
 static inline raw_spinlock_t *lock_addr(const atomic64_t *v)
 {
···
 	return ret;
 }
 EXPORT_SYMBOL(atomic64_add_unless);
-
-static int init_atomic64_lock(void)
-{
-	int i;
-
-	for (i = 0; i < NR_LOCKS; ++i)
-		raw_spin_lock_init(&atomic64_lock[i].lock);
-	return 0;
-}
-
-pure_initcall(init_atomic64_lock);