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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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/sunrpc/auth.h
View File

@ -103,6 +103,7 @@ struct rpc_auth_create_args {
/* Flags for rpcauth_lookupcred() */
#define RPCAUTH_LOOKUP_NEW 0x01 /* Accept an uninitialised cred */
#define RPCAUTH_LOOKUP_RCU 0x02 /* lock-less lookup */
/*
* Client authentication ops
@ -154,6 +155,7 @@ void rpc_destroy_generic_auth(void);
void rpc_destroy_authunix(void);
struct rpc_cred * rpc_lookup_cred(void);
struct rpc_cred * rpc_lookup_cred_nonblock(void);
struct rpc_cred * rpc_lookup_machine_cred(const char *service_name);
int rpcauth_register(const struct rpc_authops *);
int rpcauth_unregister(const struct rpc_authops *);

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);

6
net/sunrpc/auth_generic.c
View File

@ -38,6 +38,12 @@ struct rpc_cred *rpc_lookup_cred(void)
}
EXPORT_SYMBOL_GPL(rpc_lookup_cred);
struct rpc_cred *rpc_lookup_cred_nonblock(void)
{
return rpcauth_lookupcred(&generic_auth, RPCAUTH_LOOKUP_RCU);
}
EXPORT_SYMBOL_GPL(rpc_lookup_cred_nonblock);
/*
* Public call interface for looking up machine creds.
*/

2
net/sunrpc/auth_null.c
View File

@ -35,6 +35,8 @@ nul_destroy(struct rpc_auth *auth)
static struct rpc_cred *
nul_lookup_cred(struct rpc_auth *auth, struct auth_cred *acred, int flags)
{
if (flags & RPCAUTH_LOOKUP_RCU)
return &null_cred;
return get_rpccred(&null_cred);
}