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Subject[RFC PATCH v2 1/2] fscrypt: remove d_lock on reading DCACHE_ENCRYPTED_WITH_KEY
Date
It seems there is no need to take d_lock when accessing
dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY in
fscrypt_d_revalidate. It only needs to be serialized for updating.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---

Change log v2:
- Fix negative dentry (NULL d_inode) issue as Eric pointed out;
- Fix to use '__lockref_is_dead()' as Eric pointed out before;

[original message]
Hi,
At glance, I have no idea why fscrypt_d_revalidate disables
RCU-lookup. Therefore I made patches to raise a question and
do some test (eg. fsstress w/ and w/o drop_caches) and it
seems to work.

Thanks,
Gao Xiang

fs/crypto/crypto.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index 0f46cf550907..b38c574f70ac 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -329,9 +329,8 @@ static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
return 0;
}

- spin_lock(&dentry->d_lock);
- cached_with_key = dentry->d_flags & DCACHE_ENCRYPTED_WITH_KEY;
- spin_unlock(&dentry->d_lock);
+ cached_with_key = READ_ONCE(dentry->d_flags) &
+ DCACHE_ENCRYPTED_WITH_KEY;
dir_has_key = (d_inode(dir)->i_crypt_info != NULL);
dput(dir);

--
2.14.4
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