[RFC,v2,1/2] fscrypt: remove d_lock on reading DCACHE_ENCRYPTED_WITH_KEY
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Message ID 20181106122052.18507-1-gaoxiang25@huawei.com
State New
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  • [RFC,v2,1/2] fscrypt: remove d_lock on reading DCACHE_ENCRYPTED_WITH_KEY
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Commit Message

Gao Xiang Nov. 6, 2018, 12:20 p.m. UTC
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]
 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.

Gao Xiang

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

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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) &
 	dir_has_key = (d_inode(dir)->i_crypt_info != NULL);