This patch attempts to enable RCU-walk for fscrypt.
It looks harmless at glance and could have better
performance than do ref-walk only.
Signed-off-by: Gao Xiang <gaoxian...@huawei.com>
---
p.s.
In my opinion, it is better to retry for the case of
READ_ONCE(dentry->d_parent) != dir rather than just
return 0; and then do real lookup for ref-walk path...
It behaves much like a seqlock and I tend to avoid
taking d_lock as well..
Please kindly correct me if I am wrong... Thanks in advance.
Thanks,
Gao Xiang
fs/crypto/crypto.c | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index b38c574f70ac..2cc26fe9c43d 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -319,20 +319,29 @@ static int fscrypt_d_revalidate(struct dentry *dentry,
unsigned int flags)
{
struct dentry *dir;
int dir_has_key, cached_with_key;
+ struct inode *dir_inode;
- if (flags & LOOKUP_RCU)
- return -ECHILD;
+repeat:
+ rcu_read_lock();
+ dir = READ_ONCE(dentry->d_parent);
- dir = dget_parent(dentry);
- if (!IS_ENCRYPTED(d_inode(dir))) {
- dput(dir);
+ dir_inode = d_inode_rcu(dir);
+ if (!dir_inode || !IS_ENCRYPTED(dir_inode)) {
+ rcu_read_unlock();
return 0;
}
+ dir_has_key = (dir_inode->i_crypt_info != NULL);
+
+ /* original dir becomes invalid after sampling all? */
+ if (unlikely(__lockref_is_dead(&dir->d_lockref) ||
+ READ_ONCE(dentry->d_parent) != dir)) {
+ rcu_read_unlock();
+ goto repeat;
+ }
+ rcu_read_unlock();
cached_with_key = READ_ONCE(dentry->d_flags) &
DCACHE_ENCRYPTED_WITH_KEY;
- dir_has_key = (d_inode(dir)->i_crypt_info != NULL);
- dput(dir);
/*
* If the dentry was cached without the key, and it is a
--
2.14.4
