queue-6.8/net-smc-reduce-rtnl-pressure-in-smc_pnet_create_pnet.patch

   1 From 3c2681396652decff4615b9f455b9f40f19da675 Mon Sep 17 00:00:00 2001
   2 From: Sasha Levin <sashal@kernel.org>
   3 Date: Sat, 2 Mar 2024 10:07:44 +0000
   4 Subject: net/smc: reduce rtnl pressure in smc_pnet_create_pnetids_list()
   5
   6 From: Eric Dumazet <edumazet@google.com>
   7
   8 [ Upstream commit 00af2aa93b76b1bade471ad0d0525d4d29ca5cc0 ]
   9
  10 Many syzbot reports show extreme rtnl pressure, and many of them hint
  11 that smc acquires rtnl in netns creation for no good reason [1]
  12
  13 This patch returns early from smc_pnet_net_init()
  14 if there is no netdevice yet.
  15
  16 I am not even sure why smc_pnet_create_pnetids_list() even exists,
  17 because smc_pnet_netdev_event() is also calling
  18 smc_pnet_add_base_pnetid() when handling NETDEV_UP event.
  19
  20 [1] extract of typical syzbot reports
  21
  22 2 locks held by syz-executor.3/12252:
  23   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  24   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  25   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  26 2 locks held by syz-executor.4/12253:
  27   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  28   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  29   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  30 2 locks held by syz-executor.1/12257:
  31   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  32   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  33   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  34 2 locks held by syz-executor.2/12261:
  35   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  36   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  37   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  38 2 locks held by syz-executor.0/12265:
  39   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  40   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  41   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  42 2 locks held by syz-executor.3/12268:
  43   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  44   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  45   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  46 2 locks held by syz-executor.4/12271:
  47   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  48   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  49   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  50 2 locks held by syz-executor.1/12274:
  51   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  52   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  53   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  54 2 locks held by syz-executor.2/12280:
  55   #0: ffffffff8f369610 (pernet_ops_rwsem){++++}-{3:3}, at: copy_net_ns+0x4c7/0x7b0 net/core/net_namespace.c:491
  56   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_create_pnetids_list net/smc/smc_pnet.c:809 [inline]
  57   #1: ffffffff8f375b88 (rtnl_mutex){+.+.}-{3:3}, at: smc_pnet_net_init+0x10a/0x1e0 net/smc/smc_pnet.c:878
  58
  59 Signed-off-by: Eric Dumazet <edumazet@google.com>
  60 Cc: Wenjia Zhang <wenjia@linux.ibm.com>
  61 Cc: Jan Karcher <jaka@linux.ibm.com>
  62 Cc: "D. Wythe" <alibuda@linux.alibaba.com>
  63 Cc: Tony Lu <tonylu@linux.alibaba.com>
  64 Cc: Wen Gu <guwen@linux.alibaba.com>
  65 Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>
  66 Link: https://lore.kernel.org/r/20240302100744.3868021-1-edumazet@google.com
  67 Signed-off-by: Paolo Abeni <pabeni@redhat.com>
  68 Signed-off-by: Sasha Levin <sashal@kernel.org>
  69 ---
  70  net/smc/smc_pnet.c | 10 ++++++++++
  71  1 file changed, 10 insertions(+)
  72
  73 diff --git a/net/smc/smc_pnet.c b/net/smc/smc_pnet.c
  74 index 9f2c58c5a86b7..2adb92b8c4699 100644
  75 --- a/net/smc/smc_pnet.c
  76 +++ b/net/smc/smc_pnet.c
  77 @@ -806,6 +806,16 @@ static void smc_pnet_create_pnetids_list(struct net *net)
  78         u8 ndev_pnetid[SMC_MAX_PNETID_LEN];
  79         struct net_device *dev;
  80
  81 +       /* Newly created netns do not have devices.
  82 +        * Do not even acquire rtnl.
  83 +        */
  84 +       if (list_empty(&net->dev_base_head))
  85 +               return;
  86 +
  87 +       /* Note: This might not be needed, because smc_pnet_netdev_event()
  88 +        * is also calling smc_pnet_add_base_pnetid() when handling
  89 +        * NETDEV_UP event.
  90 +        */
  91         rtnl_lock();
  92         for_each_netdev(net, dev)
  93                 smc_pnet_add_base_pnetid(net, dev, ndev_pnetid);
  94 --
  95 2.43.0
  96