Subject: Re: [PATCH net-next v7 5/6] flow_offload: support get multi-subsystem block

From: Vlad Buslov <[email-masked]>
Date: Mon, 12 Aug 2019 14:11:56 +0000

On Wed 07 Aug 2019 at 04:13, [email-masked] wrote:
> From: wenxu <[email-masked]>
>
> It provide a callback list to find the blocks of tc
> and nft subsystems
>
> Signed-off-by: wenxu <[email-masked]>
> Acked-by: Jakub Kicinski <[email-masked]>
> ---
> v7: add a mutex lock for add/del flow_indr_block_ing_cb
>
>  include/net/flow_offload.h | 10 ++++++++-
>  net/core/flow_offload.c    | 51 ++++++++++++++++++++++++++++++++++------------
>  net/sched/cls_api.c        |  9 +++++++-
>  3 files changed, 55 insertions(+), 15 deletions(-)
>
> diff --git a/include/net/flow_offload.h b/include/net/flow_offload.h
> index 46b8777..e8069b6 100644
> --- a/include/net/flow_offload.h
> +++ b/include/net/flow_offload.h
> @@ -379,6 +379,15 @@ typedef void flow_indr_block_ing_cmd_t(struct net_device *dev,
>  					void *cb_priv,
>  					enum flow_block_command command);
>  
> +struct flow_indr_block_ing_entry {
> +	flow_indr_block_ing_cmd_t *cb;
> +	struct list_head	list;
> +};
> +
> +void flow_indr_add_block_ing_cb(struct flow_indr_block_ing_entry *entry);
> +
> +void flow_indr_del_block_ing_cb(struct flow_indr_block_ing_entry *entry);
> +
>  int __flow_indr_block_cb_register(struct net_device *dev, void *cb_priv,
>  				  flow_indr_block_bind_cb_t *cb,
>  				  void *cb_ident);
> @@ -395,7 +404,6 @@ void flow_indr_block_cb_unregister(struct net_device *dev,
>  				   void *cb_ident);
>  
>  void flow_indr_block_call(struct net_device *dev,
> -			  flow_indr_block_ing_cmd_t *cb,
>  			  struct flow_block_offload *bo,
>  			  enum flow_block_command command);
>  
> diff --git a/net/core/flow_offload.c b/net/core/flow_offload.c
> index 4cc18e4..64c3d4d 100644
> --- a/net/core/flow_offload.c
> +++ b/net/core/flow_offload.c
> @@ -3,6 +3,7 @@
>  #include <linux/slab.h>
>  #include <net/flow_offload.h>
>  #include <linux/rtnetlink.h>
> +#include <linux/mutex.h>
>  
>  struct flow_rule *flow_rule_alloc(unsigned int num_actions)
>  {
> @@ -282,6 +283,8 @@ int flow_block_cb_setup_simple(struct flow_block_offload *f,
>  }
>  EXPORT_SYMBOL(flow_block_cb_setup_simple);
>  
> +static LIST_HEAD(block_ing_cb_list);
> +
>  static struct rhashtable indr_setup_block_ht;
>  
>  struct flow_indr_block_cb {
> @@ -295,7 +298,6 @@ struct flow_indr_block_dev {
>  	struct rhash_head ht_node;
>  	struct net_device *dev;
>  	unsigned int refcnt;
> -	flow_indr_block_ing_cmd_t  *block_ing_cmd_cb;
>  	struct list_head cb_list;
>  };
>  
> @@ -389,6 +391,20 @@ static void flow_indr_block_cb_del(struct flow_indr_block_cb *indr_block_cb)
>  	kfree(indr_block_cb);
>  }
>  
> +static void flow_block_ing_cmd(struct net_device *dev,
> +			       flow_indr_block_bind_cb_t *cb,
> +			       void *cb_priv,
> +			       enum flow_block_command command)
> +{
> +	struct flow_indr_block_ing_entry *entry;
> +
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(entry, &block_ing_cb_list, list) {
> +		entry->cb(dev, cb, cb_priv, command);
> +	}
> +	rcu_read_unlock();
> +}

Hi,

I'm getting following incorrect rcu usage warnings with this patch
caused by rcu_read_lock in flow_block_ing_cmd:

[  401.510948] =============================
[  401.510952] WARNING: suspicious RCU usage
[  401.510993] 5.3.0-rc3+ #589 Not tainted
[  401.510996] -----------------------------
[  401.511001] include/linux/rcupdate.h:265 Illegal context switch in RCU read-side critical section!
[  401.511004]
               other info that might help us debug this:

[  401.511008]
               rcu_scheduler_active = 2, debug_locks = 1
[  401.511012] 7 locks held by test-ecmp-add-v/7576:
[  401.511015]  #0: 00000000081d71a5 (sb_writers#4){.+.+}, at: vfs_write+0x166/0x1d0
[  401.511037]  #1: 000000002bd338c3 (&of->mutex){+.+.}, at: kernfs_fop_write+0xef/0x1b0
[  401.511051]  #2: 00000000c921c634 (kn->count#317){.+.+}, at: kernfs_fop_write+0xf7/0x1b0
[  401.511062]  #3: 00000000a19cdd56 (&dev->mutex){....}, at: sriov_numvfs_store+0x6b/0x130
[  401.511079]  #4: 000000005425fa52 (pernet_ops_rwsem){++++}, at: unregister_netdevice_notifier+0x30/0x140
[  401.511092]  #5: 00000000c5822793 (rtnl_mutex){+.+.}, at: unregister_netdevice_notifier+0x35/0x140
[  401.511101]  #6: 00000000c2f3507e (rcu_read_lock){....}, at: flow_block_ing_cmd+0x5/0x130
[  401.511115]
               stack backtrace:
[  401.511121] CPU: 21 PID: 7576 Comm: test-ecmp-add-v Not tainted 5.3.0-rc3+ #589
[  401.511124] Hardware name: Supermicro SYS-2028TP-DECR/X10DRT-P, BIOS 2.0b 03/30/2017
[  401.511127] Call Trace:
[  401.511138]  dump_stack+0x85/0xc0
[  401.511146]  ___might_sleep+0x100/0x180
[  401.511154]  __mutex_lock+0x5b/0x960
[  401.511162]  ? find_held_lock+0x2b/0x80
[  401.511173]  ? __tcf_get_next_chain+0x1d/0xb0
[  401.511179]  ? mark_held_locks+0x49/0x70
[  401.511194]  ? __tcf_get_next_chain+0x1d/0xb0
[  401.511198]  __tcf_get_next_chain+0x1d/0xb0
[  401.511251]  ? uplink_rep_async_event+0x70/0x70 [mlx5_core]
[  401.511261]  tcf_block_playback_offloads+0x39/0x160
[  401.511276]  tcf_block_setup+0x1b0/0x240
[  401.511312]  ? mlx5e_rep_indr_setup_tc_cb+0xca/0x290 [mlx5_core]
[  401.511347]  ? mlx5e_rep_indr_tc_block_unbind+0x50/0x50 [mlx5_core]
[  401.511359]  tc_indr_block_get_and_ing_cmd+0x11b/0x1e0
[  401.511404]  ? mlx5e_rep_indr_tc_block_unbind+0x50/0x50 [mlx5_core]
[  401.511414]  flow_block_ing_cmd+0x7e/0x130
[  401.511453]  ? mlx5e_rep_indr_tc_block_unbind+0x50/0x50 [mlx5_core]
[  401.511462]  __flow_indr_block_cb_unregister+0x7f/0xf0
[  401.511502]  mlx5e_nic_rep_netdevice_event+0x75/0xb0 [mlx5_core]
[  401.511513]  unregister_netdevice_notifier+0xe9/0x140
[  401.511554]  mlx5e_cleanup_rep_tx+0x6f/0xe0 [mlx5_core]
[  401.511597]  mlx5e_detach_netdev+0x4b/0x60 [mlx5_core]
[  401.511637]  mlx5e_vport_rep_unload+0x71/0xc0 [mlx5_core]
[  401.511679]  esw_offloads_disable+0x5b/0x90 [mlx5_core]
[  401.511724]  mlx5_eswitch_disable.cold+0xdf/0x176 [mlx5_core]
[  401.511759]  mlx5_device_disable_sriov+0xab/0xb0 [mlx5_core]
[  401.511794]  mlx5_core_sriov_configure+0xaf/0xd0 [mlx5_core]
[  401.511805]  sriov_numvfs_store+0xf8/0x130
[  401.511817]  kernfs_fop_write+0x122/0x1b0
[  401.511826]  vfs_write+0xdb/0x1d0
[  401.511835]  ksys_write+0x65/0xe0
[  401.511847]  do_syscall_64+0x5c/0xb0
[  401.511857]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  401.511862] RIP: 0033:0x7fad892d30f8
[  401.511868] Code: 89 02 48 c7 c0 ff ff ff ff eb bb 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 25 96 0d 00 8b 00 85 c0 75 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 60 c3 0f 1f 80 00 00 00 00 48 83
 ec 28 48 89
[  401.511871] RSP: 002b:00007ffca2a9fad8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[  401.511875] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007fad892d30f8
[  401.511878] RDX: 0000000000000002 RSI: 000055afeb072a90 RDI: 0000000000000001
[  401.511881] RBP: 000055afeb072a90 R08: 00000000ffffffff R09: 000000000000000a
[  401.511884] R10: 000055afeb058710 R11: 0000000000000246 R12: 0000000000000002
[  401.511887] R13: 00007fad893a8780 R14: 0000000000000002 R15: 00007fad893a3740

I don't think it is correct approach to try to call these callbacks with
rcu protection because:

- Cls API uses sleeping locks that cannot be used in rcu read section
  (hence the included trace).

- It assumes that all implementation of classifier ops reoffload() don't
  sleep.

- And that all driver offload callbacks (both block and classifier
  setup) don't sleep, which is not the case.

I don't see any straightforward way to fix this, besides using some
other locking mechanism to protect block_ing_cb_list.

Regards,
Vlad