tipc: block BH before using dst_cache
dst_cache_get() documents it must be used with BH disabled. sysbot reported : BUG: using smp_processor_id() in preemptible [00000000] code: /21697 caller is dst_cache_get+0x3a/0xb0 net/core/dst_cache.c:68 CPU: 0 PID: 21697 Comm: Not tainted 5.7.0-rc6-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x188/0x20d lib/dump_stack.c:118 check_preemption_disabled lib/smp_processor_id.c:47 [inline] debug_smp_processor_id.cold+0x88/0x9b lib/smp_processor_id.c:57 dst_cache_get+0x3a/0xb0 net/core/dst_cache.c:68 tipc_udp_xmit.isra.0+0xb9/0xad0 net/tipc/udp_media.c:164 tipc_udp_send_msg+0x3e6/0x490 net/tipc/udp_media.c:244 tipc_bearer_xmit_skb+0x1de/0x3f0 net/tipc/bearer.c:526 tipc_enable_bearer+0xb2f/0xd60 net/tipc/bearer.c:331 __tipc_nl_bearer_enable+0x2bf/0x390 net/tipc/bearer.c:995 tipc_nl_bearer_enable+0x1e/0x30 net/tipc/bearer.c:1003 genl_family_rcv_msg_doit net/netlink/genetlink.c:673 [inline] genl_family_rcv_msg net/netlink/genetlink.c:718 [inline] genl_rcv_msg+0x627/0xdf0 net/netlink/genetlink.c:735 netlink_rcv_skb+0x15a/0x410 net/netlink/af_netlink.c:2469 genl_rcv+0x24/0x40 net/netlink/genetlink.c:746 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline] netlink_unicast+0x537/0x740 net/netlink/af_netlink.c:1329 netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918 sock_sendmsg_nosec net/socket.c:652 [inline] sock_sendmsg+0xcf/0x120 net/socket.c:672 ____sys_sendmsg+0x6bf/0x7e0 net/socket.c:2362 ___sys_sendmsg+0x100/0x170 net/socket.c:2416 __sys_sendmsg+0xec/0x1b0 net/socket.c:2449 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 RIP: 0033:0x45ca29 Fixes: e9c1a793 ("tipc: add dst_cache support for udp media") Cc: Xin Long <lucien.xin@gmail.com> Cc: Jon Maloy <jon.maloy@ericsson.com> Signed-off-by:Eric Dumazet <edumazet@google.com> Reported-by: