1/ rcu_dereference isn't correct: that field isn't
RCU protected. It could potentially change at any time
so ACCESS_ONCE might be justified.
changes to ->d_parent are protected by ->d_seq. However
that isn't always checked after ->d_revalidate is called,
so it is safest to keep the double-check that ->d_parent
hasn't changed at the end of these functions.
2/ in nfs4_lookup_revalidate, "->d_parent" was forgotten.
So 'parent' was not the parent of 'dentry'.
This fails safe is the context is that dentry->d_inode is
NULL, and the result of parent->d_inode being NULL is
that ECHILD is returned, which is always safe.
Reported-by: kbuild test robot <fengguang.wu@xxxxxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
fs/nfs/dir.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index e754d205ea54..0295f78f2976 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1102,7 +1102,7 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
int error;
if (flags & LOOKUP_RCU) {
- parent = rcu_dereference(dentry->d_parent);
+ parent = ACCESS_ONCE(dentry->d_parent);
dir = ACCESS_ONCE(parent->d_inode);
if (!dir)
return -ECHILD;
@@ -1184,7 +1184,7 @@ out_set_verifier:
nfs_advise_use_readdirplus(dir);
out_valid_noent:
if (flags & LOOKUP_RCU) {
- if (parent != rcu_dereference(dentry->d_parent))
+ if (parent != ACCESS_ONCE(dentry->d_parent))
return -ECHILD;
} else
dput(parent);
@@ -1585,7 +1585,7 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags)
struct inode *dir;
if (flags & LOOKUP_RCU) {
- parent = rcu_dereference(dentry);
+ parent = ACCESS_ONCE(dentry->d_parent);
dir = ACCESS_ONCE(parent->d_inode);
if (!dir)
return -ECHILD;
@@ -1599,7 +1599,7 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags)
ret = -ECHILD;
if (!(flags & LOOKUP_RCU))
dput(parent);
- else if (parent != rcu_dereference(dentry))
+ else if (parent != ACCESS_ONCE(dentry->d_parent))
return -ECHILD;
goto out;
}
--
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