[PATCH 4.20 47/50] libceph: avoid KEEPALIVE_PENDING races in ceph_con_keepalive()

Greg Kroah-Hartman
2019-02-13T18:46:55Z

From: Ilya Dryomov <idryomov@gmail.com>

commit 4aac9228d16458cedcfd90c7fb37211cf3653ac3 upstream.

con_fault() can transition the connection into STANDBY right after
ceph_con_keepalive() clears STANDBY in clear_standby():

libceph user thread ceph-msgr worker

ceph_con_keepalive()
mutex_lock(&con->mutex)
clear_standby(con)
mutex_unlock(&con->mutex)
mutex_lock(&con->mutex)
con_fault()
...
if KEEPALIVE_PENDING isn't set
set state to STANDBY
...
mutex_unlock(&con->mutex)
set KEEPALIVE_PENDING
set WRITE_PENDING

This triggers warnings in clear_standby() when either ceph_con_send()
or ceph_con_keepalive() get to clearing STANDBY next time.

I don't see a reason to condition queue_con() call on the previous
value of KEEPALIVE_PENDING, so move the setting of KEEPALIVE_PENDING
into the critical section -- unlike WRITE_PENDING, KEEPALIVE_PENDING
could have been a non-atomic flag.

Reported-by: syzbot+acdeb633f6211ccdf886@syzkaller.appspotmail.com
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Tested-by: Myungho Jung <mhjungk@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/ceph/messenger.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -3219,9 +3219,10 @@ void ceph_con_keepalive(struct ceph_conn
dout("con_keepalive %p\n", con);
mutex_lock(&con->mutex);
clear_standby(con);
+ con_flag_set(con, CON_FLAG_KEEPALIVE_PENDING);
mutex_unlock(&con->mutex);
- if (con_flag_test_and_set(con, CON_FLAG_KEEPALIVE_PENDING) == 0 &&
- con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
+
+ if (con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
queue_con(con);
}
EXPORT_SYMBOL(ceph_con_keepalive);