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

From: wenxu <[email-masked]>
Date: Wed, 14 Aug 2019 10:50:47 +0800

On 8/12/2019 10:11 PM, Vlad Buslov wrote:
>
>> +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

Maybe get the  mutex flow_indr_block_ing_cb_lock for both lookup, add, delete? 

the callbacks_lists. the add and delete is work only on modules init case. So the

lookup is also not frequently(ony [un]register) and can protect with the locks.