Re: [PATCH v3 13/16] fscrypt: allow multiple extents to reference one info

["Luís Henriques" <lhenriques@suse.de>]

Sweet Tea Dorminy <sweettea-kernel@dorminy.me> writes:

> btrfs occasionally splits in-memory extents while holding a mutex. This
> means we can't just copy the info, since setting up a new inlinecrypt
> key requires taking a semaphore. Thus adding a mechanism to split
> extents and merely take a new reference on the info is necessary.
>
> Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
> ---
>  fs/crypto/fscrypt_private.h |  5 +++++
>  fs/crypto/keysetup.c        | 18 +++++++++++++++++-
>  include/linux/fscrypt.h     |  2 ++
>  3 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
> index cd29c71b4349..03be2c136c0e 100644
> --- a/fs/crypto/fscrypt_private.h
> +++ b/fs/crypto/fscrypt_private.h
> @@ -287,6 +287,11 @@ struct fscrypt_info {
>  
>  	/* Hashed inode number.  Only set for IV_INO_LBLK_32 */
>  	u32 ci_hashed_ino;
> +
> +	/* Reference count. Normally 1, unless a extent info is shared by
> +	 * several virtual extents.
> +	 */
> +	refcount_t refs;
>  };
>  
>  typedef enum {
> diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
> index 8d50716bdf11..12c3851b7cd6 100644
> --- a/fs/crypto/keysetup.c
> +++ b/fs/crypto/keysetup.c
> @@ -598,7 +598,7 @@ static void put_crypt_info(struct fscrypt_info *ci)
>  {
>  	struct fscrypt_master_key *mk;
>  
> -	if (!ci)
> +	if (!ci || !refcount_dec_and_test(&ci->refs))
>  		return;
>  
>  	if (ci->ci_enc_key) {
> @@ -686,6 +686,7 @@ fscrypt_setup_encryption_info(struct inode *inode,
>  	crypt_info->ci_inode = inode;
>  	crypt_info->ci_sb = inode->i_sb;
>  	crypt_info->ci_policy = *policy;
> +	refcount_set(&crypt_info->refs, 1);
>  	memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
>  
>  	mode = select_encryption_mode(&crypt_info->ci_policy, inode);
> @@ -1046,6 +1047,21 @@ int fscrypt_load_extent_info(struct inode *inode, void *buf, size_t len,
>  }
>  EXPORT_SYMBOL_GPL(fscrypt_load_extent_info);
>  
> +/**
> + * fscrypt_get_extent_info_ref() - mark a second extent using the same info
> + * @info: the info to be used by another extent
> + *
> + * Sometimes, an existing extent must be split into multiple extents in memory.
> + * In such a case, this function allows multiple extents to use the same extent
> + * info without allocating or taking any lock, which is necessary in certain IO
> + * paths.
> + */
> +void fscrypt_get_extent_info_ref(struct fscrypt_info *info)
> +{
> +	if (info)
> +		refcount_inc(&info->refs);
> +}
> +

There's an EXPORT_SYMBOL_GPL() missing here, right?

Cheers,
-- 
Luís

> 
>  /**
>   * fscrypt_put_encryption_info() - free most of an inode's fscrypt data
>   * @inode: an inode being evicted
> diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
> index 4ba624beea91..b67054a2c965 100644
> --- a/include/linux/fscrypt.h
> +++ b/include/linux/fscrypt.h
> @@ -370,6 +370,8 @@ void fscrypt_free_extent_info(struct fscrypt_info **info_ptr);
>  int fscrypt_load_extent_info(struct inode *inode, void *buf, size_t len,
>  			     struct fscrypt_info **info_ptr);
>  
> +void fscrypt_get_extent_info_ref(struct fscrypt_info *info);
> +
>  /* fname.c */
>  int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
>  			  u8 *out, unsigned int olen);
> -- 
>
> 2.41.0
>