linux/net/unix
Kuniyuki Iwashima 9acbc584c3 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>
2021-11-26 18:01:58 -08:00
..
af_unix.c af_unix: Relax race in unix_autobind(). 2021-11-26 18:01:58 -08:00
diag.c af_unix: Replace the big lock with small locks. 2021-11-26 18:01:58 -08:00
garbage.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 62 2019-05-24 17:36:46 +02:00
Kconfig af_unix: Add OOB support 2021-08-04 09:55:52 +01:00
Makefile af_unix: Implement ->psock_update_sk_prot() 2021-07-15 18:17:50 -07:00
scm.c io_uring: move io_uring_get_socket() into io_uring.h 2020-09-30 20:32:33 -06:00
scm.h net: split out functions related to registering inflight socket files 2019-02-28 08:24:23 -07:00
sysctl_net_unix.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
unix_bpf.c net: Implement ->sock_is_readable() for UDP and AF_UNIX 2021-10-26 12:29:33 -07:00