Return-Path: linux-nfs-owner@vger.kernel.org Received: from cantor2.suse.de ([195.135.220.15]:53423 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752443AbaGNBbY (ORCPT ); Sun, 13 Jul 2014 21:31:24 -0400 From: NeilBrown To: Trond Myklebust Date: Mon, 14 Jul 2014 11:28:20 +1000 Subject: [PATCH 4/7] NFS: support RCU_WALK in nfs_permission() Cc: linux-nfs@vger.kernel.org Message-ID: <20140714012820.12562.43671.stgit@notabene.brown> In-Reply-To: <20140714011630.12562.1940.stgit@notabene.brown> References: <20140714011630.12562.1940.stgit@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: 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 --- fs/nfs/dir.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index 3c2b36acf291..ac958f29e558 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -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;