syzbot is reporting lockdep warning at rds_tcp_reset_callbacks() [1], for
commit ac3615e7f3cffe2a ("RDS: TCP: Reduce code duplication in
rds_tcp_reset_callbacks()") added cancel_delayed_work_sync() into a section
protected by lock_sock() without realizing that rds_send_xmit() might call
lock_sock().
We don't need to protect cancel_delayed_work_sync() using lock_sock(), for
even if rds_{send,recv}_worker() re-queued this work while __flush_work()
from cancel_delayed_work_sync() was waiting for this work to complete,
retried rds_{send,recv}_worker() is no-op due to the absence of RDS_CONN_UP
bit.
Link: https://syzkaller.appspot.com/bug?extid=78c55c7bc6f66e53dce2 [1]
Reported-by: syzbot <syzbot+78c55c7bc6f66e53dce2@xxxxxxxxxxxxxxxxxxxxxxxxx>
Co-developed-by: Hillf Danton <hdanton@xxxxxxxx>
Signed-off-by: Hillf Danton <hdanton@xxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Tested-by: syzbot <syzbot+78c55c7bc6f66e53dce2@xxxxxxxxxxxxxxxxxxxxxxxxx>
Fixes: ac3615e7f3cffe2a ("RDS: TCP: Reduce code duplication in rds_tcp_reset_callbacks()")
---
Hillf, why don't you propose as a formal patch after syzbot tested your patch?
Explaining as a formal patch helps us with understanding/reviewing what you thought and
how you came to your patch. I feel sorry for stealing result of your trial and error...
net/rds/tcp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 73ee2771093d..d0ff413f697c 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -166,10 +166,10 @@ void rds_tcp_reset_callbacks(struct socket *sock,
*/
atomic_set(&cp->cp_state, RDS_CONN_RESETTING);
wait_event(cp->cp_waitq, !test_bit(RDS_IN_XMIT, &cp->cp_flags));
- lock_sock(osock->sk);
/* reset receive side state for rds_tcp_data_recv() for osock */
cancel_delayed_work_sync(&cp->cp_send_w);
cancel_delayed_work_sync(&cp->cp_recv_w);
+ lock_sock(osock->sk);
if (tc->t_tinc) {
rds_inc_put(&tc->t_tinc->ti_inc);
tc->t_tinc = NULL;
--
2.34.1
