From: NeilBrown Date: Mon, 14 Jul 2014 01:28:20 +0000 (+1000) Subject: NFS: support RCU_WALK in nfs_permission() X-Git-Tag: omap-for-v3.17/fixes-against-rc2~82^2~7 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f3324a2a94c229831cfd42d871902cd4a9bd5e0f;p=pandora-kernel.git NFS: support RCU_WALK in nfs_permission() 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 Signed-off-by: Trond Myklebust --- Reading git-diff-tree failed