exfat: fix use of uninitialized spinlock on error path

syzbot reported warning message:

Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d6/0x29e lib/dump_stack.c:118
 register_lock_class+0xf06/0x1520 kernel/locking/lockdep.c:893
 __lock_acquire+0xfd/0x2ae0 kernel/locking/lockdep.c:4320
 lock_acquire+0x148/0x720 kernel/locking/lockdep.c:5029
 __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
 _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
 spin_lock include/linux/spinlock.h:354 [inline]
 exfat_cache_inval_inode+0x30/0x280 fs/exfat/cache.c:226
 exfat_evict_inode+0x124/0x270 fs/exfat/inode.c:660
 evict+0x2bb/0x6d0 fs/inode.c:576
 exfat_fill_super+0x1e07/0x27d0 fs/exfat/super.c:681
 get_tree_bdev+0x3e9/0x5f0 fs/super.c:1342
 vfs_get_tree+0x88/0x270 fs/super.c:1547
 do_new_mount fs/namespace.c:2875 [inline]
 path_mount+0x179d/0x29e0 fs/namespace.c:3192
 do_mount fs/namespace.c:3205 [inline]
 __do_sys_mount fs/namespace.c:3413 [inline]
 __se_sys_mount+0x126/0x180 fs/namespace.c:3390
 do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

If exfat_read_root() returns an error, spinlock is used in
exfat_evict_inode() without initialization. This patch combines
exfat_cache_init_inode() with exfat_inode_init_once() to initialize
spinlock by slab constructor.

Fixes: c35b6810 ("exfat: add exfat cache")
Cc: stable@vger.kernel.org # v5.7+
Reported-by: syzbot <syzbot+b91107320911a26c9a95@syzkaller.appspotmail.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>

fs/exfat/cache.c

@@ -17,7 +17,6 @@
 #include "exfat_raw.h"
 #include "exfat_fs.h"
 
-#define EXFAT_CACHE_VALID	0
 #define EXFAT_MAX_CACHE		16
 
 struct exfat_cache {
@@ -61,16 +60,6 @@ void exfat_cache_shutdown(void)
 	kmem_cache_destroy(exfat_cachep);
 }
 
-void exfat_cache_init_inode(struct inode *inode)
-{
-	struct exfat_inode_info *ei = EXFAT_I(inode);
-
-	spin_lock_init(&ei->cache_lru_lock);
-	ei->nr_caches = 0;
-	ei->cache_valid_id = EXFAT_CACHE_VALID + 1;
-	INIT_LIST_HEAD(&ei->cache_lru);
-}
-
 static inline struct exfat_cache *exfat_cache_alloc(void)
 {
 	return kmem_cache_alloc(exfat_cachep, GFP_NOFS);

fs/exfat/exfat_fs.h

@@ -248,6 +248,8 @@ struct exfat_sb_info {
 	struct rcu_head rcu;
 };
 
+#define EXFAT_CACHE_VALID	0
+
 /*
  * EXFAT file system inode in-memory data
  */
@@ -428,7 +430,6 @@ extern const struct dentry_operations exfat_utf8_dentry_ops;
 /* cache.c */
 int exfat_cache_init(void);
 void exfat_cache_shutdown(void);
-void exfat_cache_init_inode(struct inode *inode);
 void exfat_cache_inval_inode(struct inode *inode);
 int exfat_get_cluster(struct inode *inode, unsigned int cluster,
 		unsigned int *fclus, unsigned int *dclus,

fs/exfat/inode.c

@@ -611,8 +611,6 @@ static int exfat_fill_inode(struct inode *inode, struct exfat_dir_entry *info)
 	ei->i_crtime = info->crtime;
 	inode->i_atime = info->atime;
 
-	exfat_cache_init_inode(inode);
-
 	return 0;
 }
 

fs/exfat/super.c

@@ -376,7 +376,6 @@ static int exfat_read_root(struct inode *inode)
 	inode->i_mtime = inode->i_atime = inode->i_ctime = ei->i_crtime =
 		current_time(inode);
 	exfat_truncate_atime(&inode->i_atime);
-	exfat_cache_init_inode(inode);
 	return 0;
 }
 
@@ -763,6 +762,10 @@ static void exfat_inode_init_once(void *foo)
 {
 	struct exfat_inode_info *ei = (struct exfat_inode_info *)foo;
 
+	spin_lock_init(&ei->cache_lru_lock);
+	ei->nr_caches = 0;
+	ei->cache_valid_id = EXFAT_CACHE_VALID + 1;
+	INIT_LIST_HEAD(&ei->cache_lru);
 	INIT_HLIST_NODE(&ei->i_hash_fat);
 	inode_init_once(&ei->vfs_inode);
 }