f2fs crypto: use per-inode tfm structure

This patch applies the following ext4 patch:

  ext4 crypto: use per-inode tfm structure

As suggested by Herbert Xu, we shouldn't allocate a new tfm each time
we read or write a page.  Instead we can use a single tfm hanging off
the inode's crypt_info structure for all of our encryption needs for
that inode, since the tfm can be used by multiple crypto requests in
parallel.

Also use cmpxchg() to avoid races that could result in crypt_info
structure getting doubly allocated or doubly freed.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 7e93fcf..70cdf7b 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2016,7 +2016,7 @@
 void f2fs_end_io_crypto_work(struct f2fs_crypto_ctx *, struct bio *);
 
 /* crypto_key.c */
-void f2fs_free_encryption_info(struct inode *);
+void f2fs_free_encryption_info(struct inode *, struct f2fs_crypt_info *);
 int _f2fs_get_encryption_info(struct inode *inode);
 
 /* crypto_fname.c */
@@ -2051,7 +2051,6 @@
 	return 0;
 }
 
-int f2fs_setup_fname_crypto(struct inode *);
 void f2fs_fname_crypto_free_buffer(struct f2fs_str *);
 int f2fs_fname_setup_filename(struct inode *, const struct qstr *,
 				int lookup, struct f2fs_filename *);
@@ -2065,8 +2064,6 @@
 
 static inline int f2fs_has_encryption_key(struct inode *i) { return 0; }
 static inline int f2fs_get_encryption_info(struct inode *i) { return 0; }
-
-static inline int f2fs_setup_fname_crypto(struct inode *i) { return 0; }
 static inline void f2fs_fname_crypto_free_buffer(struct f2fs_str *p) { }
 
 static inline int f2fs_fname_setup_filename(struct inode *dir,