netdev - Re: [Patch net] smc: use RCU version of lower netdev searching

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Message-ID: <ad8da8d1-4ae4-41e2-a047-e4adc4c044f5@linux.alibaba.com>
Date: Wed, 18 Sep 2024 10:23:45 +0800
From: "D. Wythe" <alibuda@...ux.alibaba.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
 syzbot+c75d1de73d3b8b76272f@...kaller.appspotmail.com,
 Wenjia Zhang <wenjia@...ux.ibm.com>, Jan Karcher <jaka@...ux.ibm.com>,
 Tony Lu <tonylu@...ux.alibaba.com>, Wen Gu <guwen@...ux.alibaba.com>
Subject: Re: [Patch net] smc: use RCU version of lower netdev searching



On 9/14/24 11:32 AM, Cong Wang wrote:
> On Sat, Sep 14, 2024 at 10:28:15AM +0800, D. Wythe wrote:
>>
>>
>> On 9/14/24 8:53 AM, Cong Wang wrote:
>>> On Thu, Sep 12, 2024 at 02:20:47PM +0800, D. Wythe wrote:
>>>>
>>>>
>>>> On 9/12/24 8:04 AM, Cong Wang wrote:
>>>>> From: Cong Wang <cong.wang@...edance.com>
>>>>>
>>>>> Both netdev_walk_all_lower_dev() and netdev_lower_get_next() have a
>>>>> RCU version, which are netdev_walk_all_lower_dev_rcu() and
>>>>> netdev_next_lower_dev_rcu(). Switching to the RCU version would
>>>>> eliminate the need for RTL lock, thus could amend the deadlock
>>>>> complaints from syzbot. And it could also potentially speed up its
>>>>> callers like smc_connect().
>>>>>
>>>>> Reported-by: syzbot+c75d1de73d3b8b76272f@...kaller.appspotmail.com
>>>>> Closes: https://syzkaller.appspot.com/bug?extid=c75d1de73d3b8b76272f
>>>>> Cc: Wenjia Zhang <wenjia@...ux.ibm.com>
>>>>> Cc: Jan Karcher <jaka@...ux.ibm.com>
>>>>> Cc: "D. Wythe" <alibuda@...ux.alibaba.com>
>>>>> Cc: Tony Lu <tonylu@...ux.alibaba.com>
>>>>> Cc: Wen Gu <guwen@...ux.alibaba.com>
>>>>> Signed-off-by: Cong Wang <cong.wang@...edance.com>
>>>>
>>>>
>>>> Haven't looked at your code yet, but the issue you fixed doesn't exist.
>>>> The real reason is that we lacks some lockdep annotations for
>>>> IPPROTO_SMC.
>>>
>>> If you look at the code, it is not about sock lock annotations, it is
>>> about RTNL lock which of course has annotations.
>>>
>>
>> If so, please explain the deadlock issue mentioned in sysbot and
>> how it triggers deadlocks.
> 
> Sure, but what questions do you have here? To me, the lockdep output is
> self-explained. Please kindly let me know if you have any troubles
> understanding it, I am always happy to help.
> 
> Thanks.

Just explain (https://syzkaller.appspot.com/bug?extid=c75d1de73d3b8b76272f)

-> #1 (sk_lock-AF_INET6){+.+.}-{0:0}:
        lock_sock_nested+0x3a/0xf0 net/core/sock.c:3543
        lock_sock include/net/sock.h:1607 [inline]
        sockopt_lock_sock net/core/sock.c:1061 [inline]
        sockopt_lock_sock+0x54/0x70 net/core/sock.c:1052
        do_ipv6_setsockopt+0x216a/0x47b0 net/ipv6/ipv6_sockglue.c:567
        ipv6_setsockopt+0xe3/0x1a0 net/ipv6/ipv6_sockglue.c:993
        udpv6_setsockopt+0x7d/0xd0 net/ipv6/udp.c:1702
        do_sock_setsockopt+0x222/0x480 net/socket.c:2324
        __sys_setsockopt+0x1a4/0x270 net/socket.c:2347
        __do_sys_setsockopt net/socket.c:2356 [inline]
        __se_sys_setsockopt net/socket.c:2353 [inline]
        __x64_sys_setsockopt+0xbd/0x160 net/socket.c:2353
        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
        do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
        entry_SYSCALL_64_after_hwframe+0x77/0x7f

Why is that udpv6_setsockopt was reported here.

D.