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.
In nfs4_lookup_revalidate we simple avoid testing LOOKUP_RCU on the
path that simply calls nfs_lookup_revalidate() as that function
already performs the required test.
Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
fs/nfs/dir.c | 36 ++++++++++++++++++++++++------------
1 file changed, 24 insertions(+), 12 deletions(-)
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index f5509f95f261..dcec2c56fe13 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1056,14 +1056,17 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
int error;
if (flags & LOOKUP_RCU)
- return -ECHILD;
-
- parent = dget_parent(dentry);
+ parent = rcu_dereference(dentry->d_parent);
+ 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;
@@ -1078,6 +1081,9 @@ 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))
@@ -1120,7 +1126,8 @@ out_set_verifier:
/* Success: notify readdir to use READDIRPLUS */
nfs_advise_use_readdirplus(dir);
out_valid_noent:
- dput(parent);
+ if (!(flags & LOOKUP_RCU))
+ dput(parent);
dfprintk(LOOKUPCACHE, "NFS: %s(%pd2) is valid\n",
__func__, dentry);
return 1;
@@ -1147,7 +1154,8 @@ out_zap_parent:
if (check_submounts_and_drop(dentry) != 0)
goto out_valid;
- dput(parent);
+ if (!(flags & LOOKUP_RCU))
+ dput(parent);
dfprintk(LOOKUPCACHE, "NFS: %s(%pd2) is invalid\n",
__func__, dentry);
return 0;
@@ -1155,7 +1163,8 @@ out_error:
nfs_free_fattr(fattr);
nfs_free_fhandle(fhandle);
nfs4_label_free(label);
- dput(parent);
+ if (!(flags & LOOKUP_RCU))
+ dput(parent);
dfprintk(LOOKUPCACHE, "NFS: %s(%pd2) lookup returned error %d\n",
__func__, dentry, error);
return error;
@@ -1499,9 +1508,6 @@ 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))
@@ -1518,6 +1524,9 @@ 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))
@@ -2273,9 +2282,6 @@ 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)
@@ -2302,6 +2308,9 @@ 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);
@@ -2316,6 +2325,9 @@ 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);
--
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