Re: [PATCH 1/1] net: rds: fix memory leak when unload rds_rdma

[Yanjun Zhu <yanjun.zhu@oracle.com>]

Sorry. Add Håkon Bugge <haakon.bugge@oracle.com>

He told me to notice the memory leak when caches are freed.

Zhu Yanjun

On 2019/6/3 20:48, Zhu Yanjun wrote:
> When KASAN is enabled, after several rds connections are
> created, then "rmmod rds_rdma" is run. The following will
> appear.
>
> "
> BUG rds_ib_incoming (Not tainted): Objects remaining
> in rds_ib_incoming on __kmem_cache_shutdown()
>
> Call Trace:
>   dump_stack+0x71/0xab
>   slab_err+0xad/0xd0
>   __kmem_cache_shutdown+0x17d/0x370
>   shutdown_cache+0x17/0x130
>   kmem_cache_destroy+0x1df/0x210
>   rds_ib_recv_exit+0x11/0x20 [rds_rdma]
>   rds_ib_exit+0x7a/0x90 [rds_rdma]
>   __x64_sys_delete_module+0x224/0x2c0
>   ? __ia32_sys_delete_module+0x2c0/0x2c0
>   do_syscall_64+0x73/0x190
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> "
> This is rds connection memory leak. The root cause is:
> When "rmmod rds_rdma" is run, rds_ib_remove_one will call
> rds_ib_dev_shutdown to drop the rds connections.
> rds_ib_dev_shutdown will call rds_conn_drop to drop rds
> connections as below.
> "
> rds_conn_path_drop(&conn->c_path[0], false);
> "
> In the above, destroy is set to false.
> void rds_conn_path_drop(struct rds_conn_path *cp, bool destroy)
> {
>          atomic_set(&cp->cp_state, RDS_CONN_ERROR);
>
>          rcu_read_lock();
>          if (!destroy && rds_destroy_pending(cp->cp_conn)) {
>                  rcu_read_unlock();
>                  return;
>          }
>          queue_work(rds_wq, &cp->cp_down_w);
>          rcu_read_unlock();
> }
> In the above function, destroy is set to false. rds_destroy_pending
> is called. This does not move rds connections to ib_nodev_conns.
> So destroy is set to true to move rds connections to ib_nodev_conns.
> In rds_ib_unregister_client, flush_workqueue is called to make rds_wq
> finsh shutdown rds connections. The function rds_ib_destroy_nodev_conns
> is called to shutdown rds connections finally.
> Then rds_ib_recv_exit is called to destroy slab.
>
> void rds_ib_recv_exit(void)
> {
>          kmem_cache_destroy(rds_ib_incoming_slab);
>          kmem_cache_destroy(rds_ib_frag_slab);
> }
> The above slab memory leak will not occur again.
>
> >From tests,
> 256 rds connections
> [root@ca-dev14 ~]# time rmmod rds_rdma
>
> real    0m16.522s
> user    0m0.000s
> sys     0m8.152s
> 512 rds connections
> [root@ca-dev14 ~]# time rmmod rds_rdma
>
> real    0m32.054s
> user    0m0.000s
> sys     0m15.568s
>
> To rmmod rds_rdma with 256 rds connections, about 16 seconds are needed.
> And with 512 rds connections, about 32 seconds are needed.
> >From ftrace, when one rds connection is destroyed,
>
> "
>   19)               |  rds_conn_destroy [rds]() {
>   19)   7.782 us    |    rds_conn_path_drop [rds]();
>   15)               |  rds_shutdown_worker [rds]() {
>   15)               |    rds_conn_shutdown [rds]() {
>   15)   1.651 us    |      rds_send_path_reset [rds]();
>   15)   7.195 us    |    }
>   15) + 11.434 us   |  }
>   19)   2.285 us    |    rds_cong_remove_conn [rds]();
>   19) * 24062.76 us |  }
> "
> So if many rds connections will be destroyed, this function
> rds_ib_destroy_nodev_conns uses most of time.
>
> Suggested-by: Håkon Bugge <haakon.bugge@oracle.com>
> Signed-off-by: Zhu Yanjun <yanjun.zhu@oracle.com>
> ---
>   net/rds/ib.c      | 2 +-
>   net/rds/ib_recv.c | 3 +++
>   2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/net/rds/ib.c b/net/rds/ib.c
> index f9baf2d..ec05d91 100644
> --- a/net/rds/ib.c
> +++ b/net/rds/ib.c
> @@ -87,7 +87,7 @@ static void rds_ib_dev_shutdown(struct rds_ib_device *rds_ibdev)
>   
>   	spin_lock_irqsave(&rds_ibdev->spinlock, flags);
>   	list_for_each_entry(ic, &rds_ibdev->conn_list, ib_node)
> -		rds_conn_drop(ic->conn);
> +		rds_conn_path_drop(&ic->conn->c_path[0], true);
>   	spin_unlock_irqrestore(&rds_ibdev->spinlock, flags);
>   }
>   
> diff --git a/net/rds/ib_recv.c b/net/rds/ib_recv.c
> index 8946c89..3cae88c 100644
> --- a/net/rds/ib_recv.c
> +++ b/net/rds/ib_recv.c
> @@ -168,6 +168,7 @@ void rds_ib_recv_free_caches(struct rds_ib_connection *ic)
>   		list_del(&inc->ii_cache_entry);
>   		WARN_ON(!list_empty(&inc->ii_frags));
>   		kmem_cache_free(rds_ib_incoming_slab, inc);
> +		atomic_dec(&rds_ib_allocation);
>   	}
>   
>   	rds_ib_cache_xfer_to_ready(&ic->i_cache_frags);
> @@ -1057,6 +1058,8 @@ int rds_ib_recv_init(void)
>   
>   void rds_ib_recv_exit(void)
>   {
> +	WARN_ON(atomic_read(&rds_ib_allocation));
> +
>   	kmem_cache_destroy(rds_ib_incoming_slab);
>   	kmem_cache_destroy(rds_ib_frag_slab);
>   }