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| author | NeilBrown <neilb@suse.de> | 2014-07-14 05:28:20 +0400 |
|---|---|---|
| committer | Trond Myklebust <trond.myklebust@primarydata.com> | 2014-08-04 01:14:12 +0400 |
| commit | f3324a2a94c229831cfd42d871902cd4a9bd5e0f (patch) | |
| tree | 287019bb1cce4518d714574bc224eba8a8ce098c /fs | |
| parent | bd95608053b7f7813351b0defc0e3e7ef8cf2803 (diff) | |
| download | linux-f3324a2a94c229831cfd42d871902cd4a9bd5e0f.tar.xz | |
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 <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/nfs/dir.c | 28 |
1 files changed, 20 insertions, 8 deletions
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index ea12e58dfd85..8a3c36984fc4 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -2316,6 +2316,10 @@ 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; @@ -2392,15 +2396,23 @@ 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; |