@@ -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;
}
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 | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)