Commit 4aac9228 authored Jan 14, 2019 by Ilya Dryomov

libceph: avoid KEEPALIVE_PENDING races in ceph_con_keepalive()



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>

parent d95e674c

net/ceph/messenger.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -3206,9 +3206,10 @@ void ceph_con_keepalive(struct ceph_connection *con)
		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);

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