diff options
author | Kuniyuki Iwashima | 2021-11-24 11:14:31 +0900 |
---|---|---|
committer | Jakub Kicinski | 2021-11-26 18:01:58 -0800 |
commit | 9acbc584c3a4e9706703039708ec947ffc152c66 (patch) | |
tree | e337d5656b0d0e55f91ed055fd3383aa42032427 /net/unix | |
parent | afd20b9290e184c203fe22f2d6b80dc7127ba724 (diff) |
af_unix: Relax race in unix_autobind().
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>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/unix')
-rw-r--r-- | net/unix/af_unix.c | 22 |
1 files changed, 12 insertions, 10 deletions
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 5c69f0d2aab1..4d6e33bbd446 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1074,8 +1074,7 @@ 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 lastnum, ordernum; int err; err = mutex_lock_interruptible(&u->bindlock); @@ -1091,32 +1090,35 @@ 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); + ordernum = prandom_u32(); + lastnum = ordernum & 0xFFFFF; 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 == lastnum) { + /* Give up if all names seems to be in use. */ err = -ENOSPC; - kfree(addr); + unix_release_addr(addr); goto out; } + goto retry; } |