Re: [PATCH 22/23] SUNRPC: simplify auth_unix.

[Chuck Lever]

Hi Neil-


> On Nov 6, 2018, at 11:12 PM, NeilBrown <neilb@xxxxxxxx> wrote:
> 
> 1/ discard 'struct unx_cred'.  We don't need any data that
>   is not already in 'struct rpc_cred'.
> 2/ Don't keep these creds in a hash table.  When a credential
>   is needed, simply allocate it.  When not needed, discard it.
>   This can easily be faster than performing a lookup on
>   a shared hash table.

What's the basis for this claim? A memory allocation disables and
enables IRQs. That definitely hits a resource that is globally
shared.

In addition, the comment near unx_marshal suggests we should
cache the marshaled on-the-wire version of the credential instead
of building it in the RPC Call buffer every time. That would
require keeping the creds around.

Have you measured a significant difference in throughput with
this patch? Have you considered improving the lookup speed of
the hash table by making the buckets into rb-trees, for example?


>   As the lookup can happen during write-out, use a mempool
>   to ensure forward progress.
>   This means that we cannot compare two credentials for
>   equality by comparing the pointers, but we never do that anyway.
> 
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
> ---
> net/sunrpc/auth.c      |    1 
> net/sunrpc/auth_unix.c |  101 +++++++++++++++---------------------------------
> 2 files changed, 32 insertions(+), 70 deletions(-)
> 
> diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
> index 867ea9834bde..a07a7c59d3a4 100644
> --- a/net/sunrpc/auth.c
> +++ b/net/sunrpc/auth.c
> @@ -651,6 +651,7 @@ rpcauth_init_cred(struct rpc_cred *cred, const struct auth_cred *acred,
> 	INIT_LIST_HEAD(&cred->cr_lru);
> 	refcount_set(&cred->cr_count, 1);
> 	cred->cr_auth = auth;
> +	cred->cr_flags = 0;
> 	cred->cr_ops = ops;
> 	cred->cr_expire = jiffies;
> 	cred->cr_cred = get_cred(acred->cred);
> diff --git a/net/sunrpc/auth_unix.c b/net/sunrpc/auth_unix.c
> index bff113a411e0..387f6b3ffbea 100644
> --- a/net/sunrpc/auth_unix.c
> +++ b/net/sunrpc/auth_unix.c
> @@ -11,16 +11,11 @@
> #include <linux/types.h>
> #include <linux/sched.h>
> #include <linux/module.h>
> +#include <linux/mempool.h>
> #include <linux/sunrpc/clnt.h>
> #include <linux/sunrpc/auth.h>
> #include <linux/user_namespace.h>
> 
> -struct unx_cred {
> -	struct rpc_cred		uc_base;
> -	kgid_t			uc_gid;
> -	kgid_t			uc_gids[UNX_NGROUPS];
> -};
> -#define uc_uid			uc_base.cr_uid
> 
> #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
> # define RPCDBG_FACILITY	RPCDBG_AUTH
> @@ -28,6 +23,7 @@ struct unx_cred {
> 
> static struct rpc_auth		unix_auth;
> static const struct rpc_credops	unix_credops;
> +static mempool_t		*unix_pool;
> 
> static struct rpc_auth *
> unx_create(const struct rpc_auth_create_args *args, struct rpc_clnt *clnt)
> @@ -42,15 +38,6 @@ static void
> unx_destroy(struct rpc_auth *auth)
> {
> 	dprintk("RPC:       destroying UNIX authenticator %p\n", auth);
> -	rpcauth_clear_credcache(auth->au_credcache);
> -}
> -
> -static int
> -unx_hash_cred(struct auth_cred *acred, unsigned int hashbits)
> -{
> -	return hash_64(from_kgid(&init_user_ns, acred->cred->fsgid) |
> -		((u64)from_kuid(&init_user_ns, acred->cred->fsuid) <<
> -			(sizeof(gid_t) * 8)), hashbits);
> }
> 
> /*
> @@ -59,53 +46,24 @@ unx_hash_cred(struct auth_cred *acred, unsigned int hashbits)
> static struct rpc_cred *
> unx_lookup_cred(struct rpc_auth *auth, struct auth_cred *acred, int flags)
> {
> -	return rpcauth_lookup_credcache(auth, acred, flags, GFP_NOFS);
> -}
> -
> -static struct rpc_cred *
> -unx_create_cred(struct rpc_auth *auth, struct auth_cred *acred, int flags, gfp_t gfp)
> -{
> -	struct unx_cred	*cred;
> -	unsigned int groups = 0;
> -	unsigned int i;
> +	struct rpc_cred *ret = mempool_alloc(unix_pool, GFP_NOFS);
> 
> 	dprintk("RPC:       allocating UNIX cred for uid %d gid %d\n",
> 			from_kuid(&init_user_ns, acred->cred->fsuid),
> 			from_kgid(&init_user_ns, acred->cred->fsgid));
> 
> -	if (!(cred = kmalloc(sizeof(*cred), gfp)))
> -		return ERR_PTR(-ENOMEM);
> -
> -	rpcauth_init_cred(&cred->uc_base, acred, auth, &unix_credops);
> -	cred->uc_base.cr_flags = 1UL << RPCAUTH_CRED_UPTODATE;
> -
> -	if (acred->cred && acred->cred->group_info != NULL)
> -		groups = acred->cred->group_info->ngroups;
> -	if (groups > UNX_NGROUPS)
> -		groups = UNX_NGROUPS;
> -
> -	cred->uc_gid = acred->cred->fsgid;
> -	for (i = 0; i < groups; i++)
> -		cred->uc_gids[i] = acred->cred->group_info->gid[i];
> -	if (i < UNX_NGROUPS)
> -		cred->uc_gids[i] = INVALID_GID;
> -
> -	return &cred->uc_base;
> -}
> -
> -static void
> -unx_free_cred(struct unx_cred *unx_cred)
> -{
> -	dprintk("RPC:       unx_free_cred %p\n", unx_cred);
> -	put_cred(unx_cred->uc_base.cr_cred);
> -	kfree(unx_cred);
> +	rpcauth_init_cred(ret, acred, auth, &unix_credops);
> +	ret->cr_flags = 1UL << RPCAUTH_CRED_UPTODATE;
> +	return ret;
> }
> 
> static void
> unx_free_cred_callback(struct rcu_head *head)
> {
> -	struct unx_cred *unx_cred = container_of(head, struct unx_cred, uc_base.cr_rcu);
> -	unx_free_cred(unx_cred);
> +	struct rpc_cred *rpc_cred = container_of(head, struct rpc_cred, cr_rcu);
> +	dprintk("RPC:       unx_free_cred %p\n", rpc_cred);
> +	put_cred(rpc_cred->cr_cred);
> +	mempool_free(rpc_cred, unix_pool);
> }
> 
> static void
> @@ -115,30 +73,32 @@ unx_destroy_cred(struct rpc_cred *cred)
> }
> 
> /*
> - * Match credentials against current process creds.
> - * The root_override argument takes care of cases where the caller may
> - * request root creds (e.g. for NFS swapping).
> + * Match credentials against current the auth_cred.
>  */
> static int
> -unx_match(struct auth_cred *acred, struct rpc_cred *rcred, int flags)
> +unx_match(struct auth_cred *acred, struct rpc_cred *cred, int flags)
> {
> -	struct unx_cred	*cred = container_of(rcred, struct unx_cred, uc_base);
> 	unsigned int groups = 0;
> 	unsigned int i;
> 
> +	if (cred->cr_cred == acred->cred)
> +		return 1;
> 
> -	if (!uid_eq(cred->uc_uid, acred->cred->fsuid) || !gid_eq(cred->uc_gid, acred->cred->fsgid))
> +	if (!uid_eq(cred->cr_cred->fsuid, acred->cred->fsuid) || !gid_eq(cred->cr_cred->fsgid, acred->cred->fsgid))
> 		return 0;
> 
> 	if (acred->cred && acred->cred->group_info != NULL)
> 		groups = acred->cred->group_info->ngroups;
> 	if (groups > UNX_NGROUPS)
> 		groups = UNX_NGROUPS;
> +	if (cred->cr_cred->group_info == NULL)
> +		return groups == 0;
> +	if (groups != cred->cr_cred->group_info->ngroups)
> +		return 0;
> +
> 	for (i = 0; i < groups ; i++)
> -		if (!gid_eq(cred->uc_gids[i], acred->cred->group_info->gid[i]))
> +		if (!gid_eq(cred->cr_cred->group_info->gid[i], acred->cred->group_info->gid[i]))
> 			return 0;
> -	if (groups < UNX_NGROUPS && gid_valid(cred->uc_gids[groups]))
> -		return 0;
> 	return 1;
> }
> 
> @@ -150,9 +110,10 @@ static __be32 *
> unx_marshal(struct rpc_task *task, __be32 *p)
> {
> 	struct rpc_clnt	*clnt = task->tk_client;
> -	struct unx_cred	*cred = container_of(task->tk_rqstp->rq_cred, struct unx_cred, uc_base);
> +	struct rpc_cred	*cred = task->tk_rqstp->rq_cred;
> 	__be32		*base, *hold;
> 	int		i;
> +	struct group_info *gi = cred->cr_cred->group_info;
> 
> 	*p++ = htonl(RPC_AUTH_UNIX);
> 	base = p++;
> @@ -163,11 +124,12 @@ unx_marshal(struct rpc_task *task, __be32 *p)
> 	 */
> 	p = xdr_encode_array(p, clnt->cl_nodename, clnt->cl_nodelen);
> 
> -	*p++ = htonl((u32) from_kuid(&init_user_ns, cred->uc_uid));
> -	*p++ = htonl((u32) from_kgid(&init_user_ns, cred->uc_gid));
> +	*p++ = htonl((u32) from_kuid(&init_user_ns, cred->cr_cred->fsuid));
> +	*p++ = htonl((u32) from_kgid(&init_user_ns, cred->cr_cred->fsgid));
> 	hold = p++;
> -	for (i = 0; i < UNX_NGROUPS && gid_valid(cred->uc_gids[i]); i++)
> -		*p++ = htonl((u32) from_kgid(&init_user_ns, cred->uc_gids[i]));
> +	if (gi)
> +		for (i = 0; i < UNX_NGROUPS && i < gi->ngroups; i++)
> +			*p++ = htonl((u32) from_kgid(&init_user_ns, gi->gid[i]));
> 	*hold = htonl(p - hold - 1);		/* gid array length */
> 	*base = htonl((p - base - 1) << 2);	/* cred length */
> 
> @@ -214,12 +176,13 @@ unx_validate(struct rpc_task *task, __be32 *p)
> 
> int __init rpc_init_authunix(void)
> {
> -	return rpcauth_init_credcache(&unix_auth);
> +	unix_pool = mempool_create_kmalloc_pool(16, sizeof(struct rpc_cred));
> +	return unix_pool ? 0 : -ENOMEM;
> }
> 
> void rpc_destroy_authunix(void)
> {
> -	rpcauth_destroy_credcache(&unix_auth);
> +	mempool_destroy(unix_pool);
> }
> 
> const struct rpc_authops authunix_ops = {
> @@ -228,9 +191,7 @@ const struct rpc_authops authunix_ops = {
> 	.au_name	= "UNIX",
> 	.create		= unx_create,
> 	.destroy	= unx_destroy,
> -	.hash_cred	= unx_hash_cred,
> 	.lookup_cred	= unx_lookup_cred,
> -	.crcreate	= unx_create_cred,
> };
> 
> static
> 
> 

--
Chuck Lever