NFS: fix two problems in lookup_revalidate in RCU-walk (50d77739) · Commits · 戴 / test

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@intel.com> Signed-off-by:

NeilBrown <neilb@suse.de> Signed-off-by:

Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/dir.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -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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