• Ben Hutchings's avatar
    ipv6: addrconf: Avoid calling netdevice notifiers with RCU read-side lock · 4acd4945
    Ben Hutchings authored
    Cong Wang reports that lockdep detected suspicious RCU usage while
    enabling IPV6 forwarding:
    
     [ 1123.310275] ===============================
     [ 1123.442202] [ INFO: suspicious RCU usage. ]
     [ 1123.558207] 3.6.0-rc1+ #109 Not tainted
     [ 1123.665204] -------------------------------
     [ 1123.768254] include/linux/rcupdate.h:430 Illegal context switch in RCU read-side critical section!
     [ 1123.992320]
     [ 1123.992320] other info that might help us debug this:
     [ 1123.992320]
     [ 1124.307382]
     [ 1124.307382] rcu_scheduler_active = 1, debug_locks = 0
     [ 1124.522220] 2 locks held by sysctl/5710:
     [ 1124.648364]  #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff81768498>] rtnl_trylock+0x15/0x17
     [ 1124.882211]  #1:  (rcu_read_lock){.+.+.+}, at: [<ffffffff81871df8>] rcu_lock_acquire+0x0/0x29
     [ 1125.085209]
     [ 1125.085209] stack backtrace:
     [ 1125.332213] Pid: 5710, comm: sysctl Not tainted 3.6.0-rc1+ #109
     [ 1125.441291] Call Trace:
     [ 1125.545281]  [<ffffffff8109d915>] lockdep_rcu_suspicious+0x109/0x112
     [ 1125.667212]  [<ffffffff8107c240>] rcu_preempt_sleep_check+0x45/0x47
     [ 1125.781838]  [<ffffffff8107c260>] __might_sleep+0x1e/0x19b
    [...]
     [ 1127.445223]  [<ffffffff81757ac5>] call_netdevice_notifiers+0x4a/0x4f
    [...]
     [ 1127.772188]  [<ffffffff8175e125>] dev_disable_lro+0x32/0x6b
     [ 1127.885174]  [<ffffffff81872d26>] dev_forward_change+0x30/0xcb
     [ 1128.013214]  [<ffffffff818738c4>] addrconf_forward_change+0x85/0xc5
    [...]
    
    addrconf_forward_change() uses RCU iteration over the netdev list,
    which is unnecessary since it already holds the RTNL lock.  We also
    cannot reasonably require netdevice notifier functions not to sleep.
    Reported-by: default avatarCong Wang <amwang@redhat.com>
    Signed-off-by: default avatarBen Hutchings <bhutchings@solarflare.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    4acd4945
addrconf.c 115 KB