netdev - Re: [PATCH net 2/2] net: sched: sample: allow accessing psample

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Message-ID: <2f112b31-a1f5-6e4f-9c48-ebc5c4dac0a9@netronome.com>
Date:   Mon, 5 Aug 2019 12:39:04 +0100
From:   Pieter Jansen van Vuuren <pieter.jansenvanvuuren@...ronome.com>
To:     Vlad Buslov <vladbu@...lanox.com>, netdev@...r.kernel.org
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        davem@...emloft.net
Subject: Re: [PATCH net 2/2] net: sched: sample: allow accessing psample_group
 with rtnl

On 2019/08/03 14:36, Vlad Buslov wrote:
> Recently implemented support for sample action in flow_offload infra leads
> to following rcu usage warning:
> 
> [ 1938.234856] =============================
> [ 1938.234858] WARNING: suspicious RCU usage
> [ 1938.234863] 5.3.0-rc1+ #574 Not tainted
> [ 1938.234866] -----------------------------
> [ 1938.234869] include/net/tc_act/tc_sample.h:47 suspicious rcu_dereference_check() usage!
> [ 1938.234872]
>                other info that might help us debug this:
> 
> [ 1938.234875]
>                rcu_scheduler_active = 2, debug_locks = 1
> [ 1938.234879] 1 lock held by tc/19540:
> [ 1938.234881]  #0: 00000000b03cb918 (rtnl_mutex){+.+.}, at: tc_new_tfilter+0x47c/0x970
> [ 1938.234900]
>                stack backtrace:
> [ 1938.234905] CPU: 2 PID: 19540 Comm: tc Not tainted 5.3.0-rc1+ #574
> [ 1938.234908] Hardware name: Supermicro SYS-2028TP-DECR/X10DRT-P, BIOS 2.0b 03/30/2017
> [ 1938.234911] Call Trace:
> [ 1938.234922]  dump_stack+0x85/0xc0
> [ 1938.234930]  tc_setup_flow_action+0xed5/0x2040
> [ 1938.234944]  fl_hw_replace_filter+0x11f/0x2e0 [cls_flower]
> [ 1938.234965]  fl_change+0xd24/0x1b30 [cls_flower]
> [ 1938.234990]  tc_new_tfilter+0x3e0/0x970
> [ 1938.235021]  ? tc_del_tfilter+0x720/0x720
> [ 1938.235028]  rtnetlink_rcv_msg+0x389/0x4b0
> [ 1938.235038]  ? netlink_deliver_tap+0x95/0x400
> [ 1938.235044]  ? rtnl_dellink+0x2d0/0x2d0
> [ 1938.235053]  netlink_rcv_skb+0x49/0x110
> [ 1938.235063]  netlink_unicast+0x171/0x200
> [ 1938.235073]  netlink_sendmsg+0x224/0x3f0
> [ 1938.235091]  sock_sendmsg+0x5e/0x60
> [ 1938.235097]  ___sys_sendmsg+0x2ae/0x330
> [ 1938.235111]  ? __handle_mm_fault+0x12cd/0x19e0
> [ 1938.235125]  ? __handle_mm_fault+0x12cd/0x19e0
> [ 1938.235138]  ? find_held_lock+0x2b/0x80
> [ 1938.235147]  ? do_user_addr_fault+0x22d/0x490
> [ 1938.235160]  __sys_sendmsg+0x59/0xa0
> [ 1938.235178]  do_syscall_64+0x5c/0xb0
> [ 1938.235187]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [ 1938.235192] RIP: 0033:0x7ff9a4d597b8
> [ 1938.235197] 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 65 8f 0c 00 8b 00 85 c0 75 17 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83
>  ec 28 89 54
> [ 1938.235200] RSP: 002b:00007ffcfe381c48 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> [ 1938.235205] RAX: ffffffffffffffda RBX: 000000005d4497f9 RCX: 00007ff9a4d597b8
> [ 1938.235208] RDX: 0000000000000000 RSI: 00007ffcfe381cb0 RDI: 0000000000000003
> [ 1938.235211] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000006
> [ 1938.235214] R10: 0000000000404ec2 R11: 0000000000000246 R12: 0000000000000001
> [ 1938.235217] R13: 0000000000480640 R14: 0000000000000012 R15: 0000000000000001
> 
> Change tcf_sample_psample_group() helper to allow using it from both rtnl
> and rcu protected contexts.
> 
> Fixes: a7a7be6087b0 ("net/sched: add sample action to the hardware intermediate representation")
> Signed-off-by: Vlad Buslov <vladbu@...lanox.com>

Thanks
Reviewed-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@...ronome.com>