netdev - Re: [PATCH iproute2-rc 1/2] rdma: Fix core dump when pretty is used

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Date: Tue, 2 Jan 2024 15:44:29 +0800
From: Chengchang Tang <tangchengchang@...wei.com>
To: Stephen Hemminger <stephen@...workplumber.org>, Junxian Huang
	<huangjunxian6@...ilicon.com>
CC: <jgg@...pe.ca>, <leon@...nel.org>, <dsahern@...il.com>,
	<netdev@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<linuxarm@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH iproute2-rc 1/2] rdma: Fix core dump when pretty is used



On 2023/12/30 1:21, Stephen Hemminger wrote:
> On Fri, 29 Dec 2023 14:52:40 +0800
> Junxian Huang <huangjunxian6@...ilicon.com> wrote:
>
>> From: Chengchang Tang <tangchengchang@...wei.com>
>>
>> There will be a core dump when pretty is used as the JSON object
>> hasn't been opened and closed properly.
>>
>> Before:
>> $ rdma res show qp -jp -dd
>> [ {
>>      "ifindex": 1,
>>      "ifname": "hns_1",
>>      "port": 1,
>>      "lqpn": 1,
>>      "type": "GSI",
>>      "state": "RTS",
>>      "sq-psn": 0,
>>      "comm": "ib_core"
>> },
>> "drv_sq_wqe_cnt": 128,
>> "drv_sq_max_gs": 2,
>> "drv_rq_wqe_cnt": 512,
>> "drv_rq_max_gs": 1,
>> rdma: json_writer.c:130: jsonw_end: Assertion `self->depth > 0' failed.
>> Aborted (core dumped)
>>
>> After:
>> $ rdma res show qp -jp -dd
>> [ {
>>          "ifindex": 2,
>>          "ifname": "hns_2",
>>          "port": 1,
>>          "lqpn": 1,
>>          "type": "GSI",
>>          "state": "RTS",
>>          "sq-psn": 0,
>>          "comm": "ib_core",{
>>              "drv_sq_wqe_cnt": 128,
>>              "drv_sq_max_gs": 2,
>>              "drv_rq_wqe_cnt": 512,
>>              "drv_rq_max_gs": 1,
>>              "drv_ext_sge_sge_cnt": 256
>>          }
>>      } ]
>>
>> Fixes: 331152752a97 ("rdma: print driver resource attributes")
>> Signed-off-by: Chengchang Tang <tangchengchang@...wei.com>
>> Signed-off-by: Junxian Huang <huangjunxian6@...ilicon.com>
> This code in rdma seems to be miking json and newline functionality
> which creates bug traps.
>
> Also the json should have same effective output in pretty and non-pretty mode.
> It looks like since pretty mode add extra object layer, the nesting of {} would be
> different.
>
> The conversion to json_print() was done but it isn't using same conventions
> as ip or tc.
>
> The correct fix needs to go deeper and hit other things.
>

Hi, Stephen,

The root cause of this issue is that close_json_object() is being called 
in newline_indent(), resulting in a mismatch
of {}.

When fixing this problem, I was unsure why a newline() is needed in 
pretty mode, so I simply kept this logic and
solved the issue of open_json_object() and close_json_object() not 
matching. However, If the output of pretty mode
and not-pretty mode should be the same, then this problem can be 
resolved by deleting this newline_indent().

I believe the original developer may not have realized that 
close_json_object() is being called in newline(), which leads
to this problem. To improve the code's readability, I would try to strip 
out close_json_obejct() from newline().

Thanks,
Chengchang Tang