On Mon, Jan 29, 2024 at 05:43:22PM -0300, Gabriel Krisman Bertazi wrote:
> Unencrypted and encrypted-dentries where the key is available don't need
> to be revalidated with regards to fscrypt, since they don't go stale
> from under VFS and the key cannot be removed for the encrypted case
> without evicting the dentry. Mark them with d_set_always_valid, to
"d_set_always_valid" doesn't appear in the diff itself.
> diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
> index 4aaf847955c0..a22997b9f35c 100644
> --- a/include/linux/fscrypt.h
> +++ b/include/linux/fscrypt.h
> @@ -942,11 +942,22 @@ static inline int fscrypt_prepare_rename(struct inode *old_dir,
> static inline void fscrypt_prepare_lookup_dentry(struct dentry *dentry,
> bool is_nokey_name)
> {
> - if (is_nokey_name) {
> - spin_lock(&dentry->d_lock);
> + spin_lock(&dentry->d_lock);
> +
> + if (is_nokey_name)
> dentry->d_flags |= DCACHE_NOKEY_NAME;
> - spin_unlock(&dentry->d_lock);
> + else if (dentry->d_flags & DCACHE_OP_REVALIDATE &&
> + dentry->d_op->d_revalidate == fscrypt_d_revalidate) {
> + /*
> + * Unencrypted dentries and encrypted dentries where the
> + * key is available are always valid from fscrypt
> + * perspective. Avoid the cost of calling
> + * fscrypt_d_revalidate unnecessarily.
> + */
> + dentry->d_flags &= ~DCACHE_OP_REVALIDATE;
> }
> +
> + spin_unlock(&dentry->d_lock);
This makes lookups in unencrypted directories start doing the
spin_lock/spin_unlock pair. Is that really necessary?
These changes also make the inline function fscrypt_prepare_lookup() very long
(when including the fscrypt_prepare_lookup_dentry() that's inlined into it).
The rule that I'm trying to follow is that to the extent that the fscrypt helper
functions are inlined, the inline part should be a fast path for unencrypted
directories. Encrypted directories should be handled out-of-line.
So looking at the original fscrypt_prepare_lookup():
static inline int fscrypt_prepare_lookup(struct inode *dir,
struct dentry *dentry,
struct fscrypt_name *fname)
{
if (IS_ENCRYPTED(dir))
return __fscrypt_prepare_lookup(dir, dentry, fname);
memset(fname, 0, sizeof(*fname));
fname->usr_fname = &dentry->d_name;
fname->disk_name.name = (unsigned char *)dentry->d_name.name;
fname->disk_name.len = dentry->d_name.len;
return 0;
}
If you could just add the DCACHE_OP_REVALIDATE clearing for dentries in
unencrypted directories just before the "return 0;", hopefully without the
spinlock, that would be good. Yes, that does mean that
__fscrypt_prepare_lookup() will have to handle it too, for the case of dentries
in encrypted directories, but that seems okay.
- Eric
