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NFS: prepare for RCU-walk support but pushing tests later in code.

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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@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
This commit is contained in:
NeilBrown 2014-07-14 11:28:20 +10:00 committed by Trond Myklebust
parent 49317a7fda
commit d51ac1a8e9
1 changed files with 33 additions and 12 deletions
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45
fs/nfs/dir.c
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@ -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))
@ -2348,9 +2366,6 @@ 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)
@ -2377,6 +2392,9 @@ 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);
@ -2391,6 +2409,9 @@ 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);