nfs_lookup_revalidate, nfs4_lookup_revalidate, and nfs_permission
all need to understand and handle RCU-walk for NFS to gain the
benefits of RCU-walk for cached information.
Currently these functions all immediately return -ECHILD
if the relevant flag (LOOKUP_RCU or MAY_NOT_BLOCK) is set.
This patch pushes those tests later in the code so that we only abort
immediately before we enter rcu-unsafe code. As subsequent patches
make that rcu-unsafe code rcu-safe, several of these new tests will
disappear.
With this patch there are several paths through the code which will no
longer return -ECHILD during an RCU-walk. However these are mostly
error paths or other uninteresting cases.
A noteworthy change in nfs_lookup_revalidate is that we don't take
(or put) the reference to ->d_parent when LOOKUP_RCU is set.
Rather we rcu_dereference ->d_parent, and check that ->d_inode
is not NULL. We also check that ->d_parent hasn't changed after
all the tests.
In nfs4_lookup_revalidate we simply avoid testing LOOKUP_RCU on the
path that only calls nfs_lookup_revalidate() as that function
already performs the required test.
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
fs/nfs/dir.c | 45 +++++++++++++++++++++++++++++++++------------
1 file changed, 33 insertions(+), 12 deletions(-)
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index c5a4a89637fb..3c2b36acf291 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1088,21 +1088,30 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
struct nfs4_label *label = NULL;
int error;
- if (flags & LOOKUP_RCU)
- return -ECHILD;
-
- parent = dget_parent(dentry);
- dir = parent->d_inode;
+ if (flags & LOOKUP_RCU) {
+ parent = rcu_dereference(dentry->d_parent);
+ dir = ACCESS_ONCE(parent->d_inode);
+ if (!dir)
+ return -ECHILD;
+ } else {
+ parent = dget_parent(dentry);
+ dir = parent->d_inode;
+ }
nfs_inc_stats(dir, NFSIOS_DENTRYREVALIDATE);
inode = dentry->d_inode;
if (!inode) {
+ if (flags & LOOKUP_RCU)
+ return -ECHILD;
+
if (nfs_neg_need_reval(dir, dentry, flags))
goto out_bad;
goto out_valid_noent;
}
if (is_bad_inode(inode)) {
+ if (flags & LOOKUP_RCU)
+ return -ECHILD;
dfprintk(LOOKUPCACHE, "%s: %pd2 has dud inode\n",
__func__, dentry);
goto out_bad;
@@ -1111,6 +1120,9 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
goto out_set_verifier;
+ if (flags & LOOKUP_RCU)
+ return -ECHILD;
+
/* Force a full look up iff the parent directory has changed */
if (!nfs_is_exclusive_create(dir, flags) && nfs_check_verifier(dir, dentry)) {
if (nfs_lookup_verify_inode(inode, flags))
@@ -1153,13 +1165,18 @@ out_set_verifier:
/* Success: notify readdir to use READDIRPLUS */
nfs_advise_use_readdirplus(dir);
out_valid_noent:
- dput(parent);
+ if (flags & LOOKUP_RCU) {
+ if (parent != rcu_dereference(dentry->d_parent))
+ return -ECHILD;
+ } else
+ dput(parent);
dfprintk(LOOKUPCACHE, "NFS: %s(%pd2) is valid\n",
__func__, dentry);
return 1;
out_zap_parent:
nfs_zap_caches(dir);
out_bad:
+ WARN_ON(flags & LOOKUP_RCU);
nfs_free_fattr(fattr);
nfs_free_fhandle(fhandle);
nfs4_label_free(label);
@@ -1185,6 +1202,7 @@ out_zap_parent:
__func__, dentry);
return 0;
out_error:
+ WARN_ON(flags & LOOKUP_RCU);
nfs_free_fattr(fattr);
nfs_free_fhandle(fhandle);
nfs4_label_free(label);
@@ -1532,9 +1550,6 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags)
struct inode *inode;
int ret = 0;
- if (flags & LOOKUP_RCU)
- return -ECHILD;
-
if (!(flags & LOOKUP_OPEN) || (flags & LOOKUP_DIRECTORY))
goto no_open;
if (d_mountpoint(dentry))
@@ -1551,6 +1566,9 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags)
struct dentry *parent;
struct inode *dir;
+ if (flags & LOOKUP_RCU)
+ return -ECHILD;
+
parent = dget_parent(dentry);
dir = parent->d_inode;
if (!nfs_neg_need_reval(dir, dentry, flags))
@@ -2320,9 +2338,6 @@ int nfs_permission(struct inode *inode, int mask)
struct rpc_cred *cred;
int res = 0;
- if (mask & MAY_NOT_BLOCK)
- return -ECHILD;
-
nfs_inc_stats(inode, NFSIOS_VFSACCESS);
if ((mask & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0)
@@ -2349,6 +2364,9 @@ force_lookup:
if (!NFS_PROTO(inode)->access)
goto out_notsup;
+ if (mask & MAY_NOT_BLOCK)
+ return -ECHILD;
+
cred = rpc_lookup_cred();
if (!IS_ERR(cred)) {
res = nfs_do_access(inode, cred, mask);
@@ -2363,6 +2381,9 @@ out:
inode->i_sb->s_id, inode->i_ino, mask, res);
return res;
out_notsup:
+ if (mask & MAY_NOT_BLOCK)
+ return -ECHILD;
+
res = nfs_revalidate_inode(NFS_SERVER(inode), inode);
if (res == 0)
res = generic_permission(inode, mask);
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
