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fscrypt: cache decrypted symlink target in ->i_link

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Path lookups that traverse encrypted symlink(s) are very slow because
each encrypted symlink needs to be decrypted each time it's followed.
This also involves dropping out of rcu-walk mode.

Make encrypted symlinks faster by caching the decrypted symlink target
in ->i_link.  The first call to fscrypt_get_symlink() sets it.  Then,
the existing VFS path lookup code uses the non-NULL ->i_link to take the
fast path where ->get_link() isn't called, and lookups in rcu-walk mode
remain in rcu-walk mode.

Also set ->i_link immediately when a new encrypted symlink is created.

To safely free the symlink target after an RCU grace period has elapsed,
introduce a new function fscrypt_free_inode(), and make the relevant
filesystems call it just before actually freeing the inode.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Eric Biggers 2019-04-10 13:21:15 -07:00 • committed by Theodore Ts'o
parent 4c4f7c19b3
commit 2c58d548f5
6 changed files with 68 additions and 7 deletions
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5
include/linux/fscrypt.h
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@ -128,6 +128,7 @@ extern int fscrypt_inherit_context(struct inode *, struct inode *,
/* keyinfo.c */
extern int fscrypt_get_encryption_info(struct inode *);
extern void fscrypt_put_encryption_info(struct inode *);
extern void fscrypt_free_inode(struct inode *);
/* fname.c */
extern int fscrypt_setup_filename(struct inode *, const struct qstr *,
@ -341,6 +342,10 @@ static inline void fscrypt_put_encryption_info(struct inode *inode)
return;
}
static inline void fscrypt_free_inode(struct inode *inode)
{
}
/* fname.c */
static inline int fscrypt_setup_filename(struct inode *dir,
const struct qstr *iname,