Re: [PATCH net] ipv4: ip_tunnel: Fix suspicious RCU usage warning in ip_tunnel_init_flow()

[David Ahern <dsahern@kernel.org>]

On 10/22/24 12:38 AM, Ido Schimmel wrote:
> There are code paths from which the function is called without holding
> the RCU read lock, resulting in a suspicious RCU usage warning [1].
> 
> Fix by using l3mdev_master_upper_ifindex_by_index() which will acquire
> the RCU read lock before calling
> l3mdev_master_upper_ifindex_by_index_rcu().
> 
> [1]
> WARNING: suspicious RCU usage
> 6.12.0-rc3-custom-gac8f72681cf2 #141 Not tainted
> -----------------------------
> net/core/dev.c:876 RCU-list traversed in non-reader section!!
> 
> other info that might help us debug this:
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by ip/361:
>  #0: ffffffff86fc7cb0 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg+0x377/0xf60
> 
> stack backtrace:
> CPU: 3 UID: 0 PID: 361 Comm: ip Not tainted 6.12.0-rc3-custom-gac8f72681cf2 #141
> Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0xba/0x110
>  lockdep_rcu_suspicious.cold+0x4f/0xd6
>  dev_get_by_index_rcu+0x1d3/0x210
>  l3mdev_master_upper_ifindex_by_index_rcu+0x2b/0xf0
>  ip_tunnel_bind_dev+0x72f/0xa00
>  ip_tunnel_newlink+0x368/0x7a0
>  ipgre_newlink+0x14c/0x170
>  __rtnl_newlink+0x1173/0x19c0
>  rtnl_newlink+0x6c/0xa0
>  rtnetlink_rcv_msg+0x3cc/0xf60
>  netlink_rcv_skb+0x171/0x450
>  netlink_unicast+0x539/0x7f0
>  netlink_sendmsg+0x8c1/0xd80
>  ____sys_sendmsg+0x8f9/0xc20
>  ___sys_sendmsg+0x197/0x1e0
>  __sys_sendmsg+0x122/0x1f0
>  do_syscall_64+0xbb/0x1d0
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Fixes: db53cd3d88dc ("net: Handle l3mdev in ip_tunnel_init_flow")
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
> ---
>  include/net/ip_tunnels.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>