From: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
To: "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>
Cc: Kuniyuki Iwashima <kuniyu@amazon.co.jp>,
Kuniyuki Iwashima <kuni1840@gmail.com>,
Benjamin Herrenschmidt <benh@amazon.com>,
<netdev@vger.kernel.org>
Subject: [PATCH net-next 13/13] af_unix: Relax race in unix_autobind().
Date: Sat, 6 Nov 2021 18:17:12 +0900 [thread overview]
Message-ID: <20211106091712.15206-14-kuniyu@amazon.co.jp> (raw)
In-Reply-To: <20211106091712.15206-1-kuniyu@amazon.co.jp>
When we bind an AF_UNIX socket without a name specified, the kernel selects
an available one from 0x00000 to 0xFFFFF. unix_autobind() starts searching
from a number in the 'static' variable and increments it after acquiring
two locks.
If multiple processes try autobind, they obtain the same lock and check if
a socket in the hash list has the same name. If not, one process uses it,
and all except one end up retrying the _next_ number (actually not, it may
be incremented by the other processes). The more we autobind sockets in
parallel, the longer the latency gets. We can avoid such a race by
searching for a name from a random number.
These show latency in unix_autobind() while 64 CPUs are simultaneously
autobind-ing 1024 sockets for each.
Without this patch:
usec : count distribution
0 : 1176 |*** |
2 : 3655 |*********** |
4 : 4094 |************* |
6 : 3831 |************ |
8 : 3829 |************ |
10 : 3844 |************ |
12 : 3638 |*********** |
14 : 2992 |********* |
16 : 2485 |******* |
18 : 2230 |******* |
20 : 2095 |****** |
22 : 1853 |***** |
24 : 1827 |***** |
26 : 1677 |***** |
28 : 1473 |**** |
30 : 1573 |***** |
32 : 1417 |**** |
34 : 1385 |**** |
36 : 1345 |**** |
38 : 1344 |**** |
40 : 1200 |*** |
With this patch:
usec : count distribution
0 : 1855 |****** |
2 : 6464 |********************* |
4 : 9936 |******************************** |
6 : 12107 |****************************************|
8 : 10441 |********************************** |
10 : 7264 |*********************** |
12 : 4254 |************** |
14 : 2538 |******** |
16 : 1596 |***** |
18 : 1088 |*** |
20 : 800 |** |
22 : 670 |** |
24 : 601 |* |
26 : 562 |* |
28 : 525 |* |
30 : 446 |* |
32 : 378 |* |
34 : 337 |* |
36 : 317 |* |
38 : 314 |* |
40 : 298 | |
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
---
net/unix/af_unix.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 643f0358bf7a..55d570b23475 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1075,8 +1075,7 @@ static int unix_autobind(struct sock *sk)
unsigned int new_hash, old_hash = sk->sk_hash;
struct unix_sock *u = unix_sk(sk);
struct unix_address *addr;
- unsigned int retries = 0;
- static u32 ordernum = 1;
+ u32 initnum, ordernum;
int err;
err = mutex_lock_interruptible(&u->bindlock);
@@ -1091,31 +1090,33 @@ static int unix_autobind(struct sock *sk)
if (!addr)
goto out;
+ addr->len = offsetof(struct sockaddr_un, sun_path) + 6;
addr->name->sun_family = AF_UNIX;
refcount_set(&addr->refcnt, 1);
+ initnum = ordernum = prandom_u32();
retry:
- addr->len = sprintf(addr->name->sun_path + 1, "%05x", ordernum) +
- offsetof(struct sockaddr_un, sun_path) + 1;
+ ordernum = (ordernum + 1) & 0xFFFFF;
+ sprintf(addr->name->sun_path + 1, "%05x", ordernum);
new_hash = unix_abstract_hash(addr->name, addr->len, sk->sk_type);
unix_table_double_lock(old_hash, new_hash);
- ordernum = (ordernum+1)&0xFFFFF;
if (__unix_find_socket_byname(sock_net(sk), addr->name, addr->len, new_hash)) {
unix_table_double_unlock(old_hash, new_hash);
- /*
- * __unix_find_socket_byname() may take long time if many names
+ /* __unix_find_socket_byname() may take long time if many names
* are already in use.
*/
cond_resched();
- /* Give up if all names seems to be in use. */
- if (retries++ == 0xFFFFF) {
+
+ if (ordernum == initnum) {
+ /* Give up if all names seems to be in use. */
err = -ENOSPC;
- kfree(addr);
+ unix_release_addr(addr);
goto out;
}
+
goto retry;
}
--
2.30.2
next prev parent reply other threads:[~2021-11-06 9:20 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-06 9:16 [PATCH net-next 00/13] af_unix: Replace unix_table_lock with per-hash locks Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 01/13] af_unix: Use offsetof() instead of sizeof() Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 02/13] af_unix: Pass struct sock to unix_autobind() Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 03/13] af_unix: Factorise unix_find_other() based on address types Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 04/13] af_unix: Return an error as a pointer in unix_find_other() Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 05/13] af_unix: Cut unix_validate_addr() out of unix_mkname() Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 06/13] af_unix: Copy unix_mkname() into unix_find_(bsd|abstract)() Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 07/13] af_unix: Remove unix_mkname() Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 08/13] af_unix: Allocate unix_address in unix_bind_(bsd|abstract)() Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 09/13] af_unix: Remove UNIX_ABSTRACT() macro and test sun_path[0] instead Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 10/13] af_unix: Add helpers to calculate hashes Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 11/13] af_unix: Save hash in sk_hash Kuniyuki Iwashima
2021-11-06 9:17 ` [PATCH net-next 12/13] af_unix: Replace the big lock with small locks Kuniyuki Iwashima
2021-11-10 6:39 ` [af_unix] 95e381b609: WARNING:possible_recursive_locking_detected kernel test robot
2021-11-06 9:17 ` Kuniyuki Iwashima [this message]
2021-11-08 23:10 ` [PATCH net-next 13/13] af_unix: Relax race in unix_autobind() Eric Dumazet
2021-11-09 2:24 ` Kuniyuki Iwashima
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