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

Chengchang Tang
2024-01-02T07:44:47Z

On 2023/12/30 1:21, Stephen Hemminger wrote:
> On Fri, 29 Dec 2023 14:52:40 +0800
> Junxian Huang <huangjunxian6@hisilicon.com> wrote:
>
>> From: Chengchang Tang <tangchengchang@huawei.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@huawei.com>
>> Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.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