On 5/22/20 2:18 AM, Xin Long wrote:
On Fri, May 22, 2020 at 1:55 PM Eric Dumazet <eduma...@google.com> wrote:
Resend to the list in non HTML form
On Thu, May 21, 2020 at 10:53 PM Eric Dumazet <eduma...@google.com> wrote:
On Thu, May 21, 2020 at 10:50 PM Xin Long <lucien....@gmail.com> wrote:
On Fri, May 22, 2020 at 2:30 AM Eric Dumazet <eduma...@google.com> wrote:
dst_cache_get() documents it must be used with BH disabled.
Interesting, I thought under rcu_read_lock() is enough, which calls
preempt_disable().
rcu_read_lock() does not disable BH, never.
And rcu_read_lock() does not necessarily disable preemption.
Then I need to think again if it's really worth using dst_cache here.
Also add tipc-discussion and Jon to CC list.
The suggested solution will affect all bearers, not only UDP, so it is
not a good.
Is there anything preventing us from disabling preemtion inside the
scope of the rcu lock?
///jon
Thanks.
have you checked other places where dst_cache_get() are used?
Yes, other paths are fine.
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: e9c1a793210f ("tipc: add dst_cache support for udp media")
Cc: Xin Long <lucien....@gmail.com>
Cc: Jon Maloy <jon.ma...@ericsson.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: syzbot <syzkal...@googlegroups.com>
---
net/tipc/udp_media.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
index
d6620ad535461a4d04ed5ba90569ce8b7df9f994..28a283f26a8dff24d613e6ed57e5e69d894dae66
100644
--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -161,9 +161,11 @@ static int tipc_udp_xmit(struct net *net, struct sk_buff
*skb,
struct udp_bearer *ub, struct udp_media_addr *src,
struct udp_media_addr *dst, struct dst_cache *cache)
{
- struct dst_entry *ndst = dst_cache_get(cache);
+ struct dst_entry *ndst;
int ttl, err = 0;
+ local_bh_disable();
+ ndst = dst_cache_get(cache);
if (dst->proto == htons(ETH_P_IP)) {
struct rtable *rt = (struct rtable *)ndst;
@@ -210,9 +212,11 @@ static int tipc_udp_xmit(struct net *net, struct sk_buff
*skb,
src->port, dst->port, false);
#endif
}
+ local_bh_enable();
return err;
tx_error:
+ local_bh_enable();
kfree_skb(skb);
return err;
}
--
2.27.0.rc0.183.gde8f92d652-goog
