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af_unix: dont send SCM_CREDENTIALS by default
Since commit 7361c36c52
(af_unix: Allow credentials to work across
user and pid namespaces) af_unix performance dropped a lot.
This is because we now take a reference on pid and cred in each write(),
and release them in read(), usually done from another process,
eventually from another cpu. This triggers false sharing.
# Events: 154K cycles
#
# Overhead Command Shared Object Symbol
# ........ ....... .................. .........................
#
10.40% hackbench [kernel.kallsyms] [k] put_pid
8.60% hackbench [kernel.kallsyms] [k] unix_stream_recvmsg
7.87% hackbench [kernel.kallsyms] [k] unix_stream_sendmsg
6.11% hackbench [kernel.kallsyms] [k] do_raw_spin_lock
4.95% hackbench [kernel.kallsyms] [k] unix_scm_to_skb
4.87% hackbench [kernel.kallsyms] [k] pid_nr_ns
4.34% hackbench [kernel.kallsyms] [k] cred_to_ucred
2.39% hackbench [kernel.kallsyms] [k] unix_destruct_scm
2.24% hackbench [kernel.kallsyms] [k] sub_preempt_count
1.75% hackbench [kernel.kallsyms] [k] fget_light
1.51% hackbench [kernel.kallsyms] [k]
__mutex_lock_interruptible_slowpath
1.42% hackbench [kernel.kallsyms] [k] sock_alloc_send_pskb
This patch includes SCM_CREDENTIALS information in a af_unix message/skb
only if requested by the sender, [man 7 unix for details how to include
ancillary data using sendmsg() system call]
Note: This might break buggy applications that expected SCM_CREDENTIAL
from an unaware write() system call, and receiver not using SO_PASSCRED
socket option.
If SOCK_PASSCRED is set on source or destination socket, we still
include credentials for mere write() syscalls.
Performance boost in hackbench : more than 50% gain on a 16 thread
machine (2 quad-core cpus, 2 threads per core)
hackbench 20 thread 2000
4.228 sec instead of 9.102 sec
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
parent
a9e9fd7182
commit
16e5726269
@ -49,7 +49,7 @@ static __inline__ void scm_set_cred(struct scm_cookie *scm,
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struct pid *pid, const struct cred *cred)
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{
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scm->pid = get_pid(pid);
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scm->cred = get_cred(cred);
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scm->cred = cred ? get_cred(cred) : NULL;
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cred_to_ucred(pid, cred, &scm->creds);
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}
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@ -73,8 +73,7 @@ static __inline__ void scm_destroy(struct scm_cookie *scm)
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static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
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struct scm_cookie *scm)
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{
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scm_set_cred(scm, task_tgid(current), current_cred());
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scm->fp = NULL;
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memset(scm, 0, sizeof(*scm));
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unix_get_peersec_dgram(sock, scm);
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if (msg->msg_controllen <= 0)
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return 0;
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@ -173,7 +173,7 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
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if (err)
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goto error;
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if (pid_vnr(p->pid) != p->creds.pid) {
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if (!p->pid || pid_vnr(p->pid) != p->creds.pid) {
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struct pid *pid;
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err = -ESRCH;
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pid = find_get_pid(p->creds.pid);
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@ -183,8 +183,9 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
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p->pid = pid;
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}
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if ((p->cred->euid != p->creds.uid) ||
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(p->cred->egid != p->creds.gid)) {
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if (!p->cred ||
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(p->cred->euid != p->creds.uid) ||
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(p->cred->egid != p->creds.gid)) {
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struct cred *cred;
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err = -ENOMEM;
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cred = prepare_creds();
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@ -193,7 +194,8 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
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cred->uid = cred->euid = p->creds.uid;
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cred->gid = cred->egid = p->creds.gid;
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put_cred(p->cred);
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if (p->cred)
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put_cred(p->cred);
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p->cred = cred;
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}
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break;
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@ -1324,10 +1324,9 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
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if (msg->msg_flags&MSG_OOB)
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return -EOPNOTSUPP;
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if (NULL == siocb->scm) {
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if (NULL == siocb->scm)
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siocb->scm = &scm;
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memset(&scm, 0, sizeof(scm));
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}
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err = scm_send(sock, msg, siocb->scm);
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if (err < 0)
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return err;
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@ -1381,8 +1381,10 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
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static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool send_fds)
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{
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int err = 0;
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UNIXCB(skb).pid = get_pid(scm->pid);
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UNIXCB(skb).cred = get_cred(scm->cred);
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if (scm->cred)
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UNIXCB(skb).cred = get_cred(scm->cred);
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UNIXCB(skb).fp = NULL;
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if (scm->fp && send_fds)
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err = unix_attach_fds(scm, skb);
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@ -1391,6 +1393,24 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
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return err;
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}
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/*
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* Some apps rely on write() giving SCM_CREDENTIALS
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* We include credentials if source or destination socket
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* asserted SOCK_PASSCRED.
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*/
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static void maybe_add_creds(struct sk_buff *skb, const struct socket *sock,
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const struct sock *other)
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{
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if (UNIXCB(skb).cred)
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return;
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if (test_bit(SOCK_PASSCRED, &sock->flags) ||
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!other->sk_socket ||
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test_bit(SOCK_PASSCRED, &other->sk_socket->flags)) {
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UNIXCB(skb).pid = get_pid(task_tgid(current));
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UNIXCB(skb).cred = get_current_cred();
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}
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}
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/*
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* Send AF_UNIX data.
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*/
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@ -1538,6 +1558,7 @@ restart:
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if (sock_flag(other, SOCK_RCVTSTAMP))
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__net_timestamp(skb);
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maybe_add_creds(skb, sock, other);
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skb_queue_tail(&other->sk_receive_queue, skb);
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if (max_level > unix_sk(other)->recursion_level)
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unix_sk(other)->recursion_level = max_level;
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@ -1652,6 +1673,7 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
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(other->sk_shutdown & RCV_SHUTDOWN))
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goto pipe_err_free;
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maybe_add_creds(skb, sock, other);
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skb_queue_tail(&other->sk_receive_queue, skb);
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if (max_level > unix_sk(other)->recursion_level)
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unix_sk(other)->recursion_level = max_level;
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