@@ -2288,6 +2288,10 @@ static int nfs_do_access(struct inode *inode, struct rpc_cred *cred, int mask)
if (status == 0)
goto out_cached;
+ status = -ECHILD;
+ if (mask & MAY_NOT_BLOCK)
+ goto out;
+
/* Be clever: ask server to check for all possible rights */
cache.mask = MAY_EXEC | MAY_WRITE | MAY_READ;
cache.cred = cred;
@@ -2364,15 +2368,23 @@ 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);
- put_rpccred(cred);
- } else
+ /* Always try fast lookups first */
+ rcu_read_lock();
+ cred = rpc_lookup_cred_nonblock();
+ if (!IS_ERR(cred))
+ res = nfs_do_access(inode, cred, mask|MAY_NOT_BLOCK);
+ else
res = PTR_ERR(cred);
+ rcu_read_unlock();
+ if (res == -ECHILD && !(mask & MAY_NOT_BLOCK)) {
+ /* Fast lookup failed, try the slow way */
+ cred = rpc_lookup_cred();
+ if (!IS_ERR(cred)) {
+ res = nfs_do_access(inode, cred, mask);
+ put_rpccred(cred);
+ } else
+ res = PTR_ERR(cred);
+ }
out:
if (!res && (mask & MAY_EXEC) && !execute_ok(inode))
res = -EACCES;
nfs_permission makes two calls which are not always safe in RCU_WALK, rpc_lookup_cred and nfs_do_access. The second can easily be made rcu-safe by aborting with -ECHILD before making the RPC call. The former can be made rcu-safe by calling rpc_lookup_cred_nonblock() instead. As this will almost always succeed, we use it even when RCU_WALK isn't being used as it still saves some spinlocks in a common case. We only fall back to rpc_lookup_cred() if rpc_lookup_cred_nonblock() fails and MAY_NOT_BLOCK isn't set. This optimisation (always trying rpc_lookup_cred_nonblock()) is particularly important when a security module is active. In that case inode_permission() may return -ECHILD from security_inode_permission() even though ->permission() succeeded in RCU_WALK mode. This leads to may_lookup() retrying inode_permission after performing unlazy_walk(). The spinlock that rpc_lookup_cred() takes is often more expensive than anything security_inode_permission() does, so that spinlock becomes the main bottleneck. Signed-off-by: NeilBrown <neilb@suse.de> --- fs/nfs/dir.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html