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sunrpc/auth: allow lockless (rcu) lookup of credential cache.

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The new flag RPCAUTH_LOOKUP_RCU to credential lookup avoids locking,
does not take a reference on the returned credential, and returns
-ECHILD if a simple lookup was not possible.

The returned value can only be used within an rcu_read_lock protected
region.

The main user of this is the new rpc_lookup_cred_nonblock() which
returns a pointer to the current credential which is only rcu-safe (no
ref-count held), and might return -ECHILD if allocation was required.

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 d51ac1a8e9
commit bd95608053
4 changed files with 25 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

17
net/sunrpc/auth.c
View file

@ -557,6 +557,12 @@ rpcauth_lookup_credcache(struct rpc_auth *auth, struct auth_cred * acred,
hlist_for_each_entry_rcu(entry, &cache->hashtable[nr], cr_hash) {
if (!entry->cr_ops->crmatch(acred, entry, flags))
continue;
if (flags & RPCAUTH_LOOKUP_RCU) {
if (test_bit(RPCAUTH_CRED_HASHED, &entry->cr_flags) &&
!test_bit(RPCAUTH_CRED_NEW, &entry->cr_flags))
cred = entry;
break;
}
spin_lock(&cache->lock);
if (test_bit(RPCAUTH_CRED_HASHED, &entry->cr_flags) == 0) {
spin_unlock(&cache->lock);
@ -571,6 +577,9 @@ rpcauth_lookup_credcache(struct rpc_auth *auth, struct auth_cred * acred,
if (cred != NULL)
goto found;
if (flags & RPCAUTH_LOOKUP_RCU)
return ERR_PTR(-ECHILD);
new = auth->au_ops->crcreate(auth, acred, flags);
if (IS_ERR(new)) {
cred = new;
@ -621,10 +630,14 @@ rpcauth_lookupcred(struct rpc_auth *auth, int flags)
memset(&acred, 0, sizeof(acred));
acred.uid = cred->fsuid;
acred.gid = cred->fsgid;
acred.group_info = get_group_info(((struct cred *)cred)->group_info);
if (flags & RPCAUTH_LOOKUP_RCU)
acred.group_info = rcu_dereference(cred->group_info);
else
acred.group_info = get_group_info(((struct cred *)cred)->group_info);
ret = auth->au_ops->lookup_cred(auth, &acred, flags);
put_group_info(acred.group_info);
if (!(flags & RPCAUTH_LOOKUP_RCU))
put_group_info(acred.group_info);
return ret;
}
EXPORT_SYMBOL_GPL(rpcauth_lookupcred);