Eric Biggers <ebiggers@xxxxxxxxxx> writes:
> 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.
ok, will do. IIUC, we might be able to do without the d_lock
provided there is no store tearing.
But what was the reason you need the d_lock to set DCACHE_NOKEY_NAME
during lookup? Is there a race with parallel lookup setting d_flag that
I couldn't find? Or is it another reason?
--
Gabriel Krisman Bertazi
