linux-kernel - Re: [PATCH] coresight: Defer probe when the child dev is not probed

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Message-ID: <c2c45bed-0be1-1942-1267-16f4169c4f67@quicinc.com>
Date:   Wed, 2 Mar 2022 16:05:05 +0800
From:   Jinlong Mao <quic_jinlmao@...cinc.com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>
CC:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mao Jinlong <jinlmao@....qualcomm.com>,
        <coresight@...ts.linaro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        "Tingwei Zhang" <quic_tingweiz@...cinc.com>,
        Yuanfang Zhang <quic_yuanfang@...cinc.com>,
        Tao Zhang <quic_taozha@...cinc.com>,
        Hao Zhang <quic_hazha@...cinc.com>
Subject: Re: [PATCH] coresight: Defer probe when the child dev is not probed


On 3/2/2022 10:29 AM, Jinlong Mao wrote:
>
> On 3/1/2022 11:03 PM, Suzuki K Poulose wrote:
>> Hi
>>
>> On 01/03/2022 13:30, Jinlong Mao wrote:
>>> Hi Mike,
>>>
>>> On 3/1/2022 9:15 PM, Mike Leach wrote:
>>>> Hi,
>>>>
>>>> On Tue, 1 Mar 2022 at 11:42, Jinlong Mao <quic_jinlmao@...cinc.com> 
>>>> wrote:
>>>>> On 2/28/2022 10:51 PM, Suzuki K Poulose wrote:
>>>>>
>>
>> ...
>>
>>>>>
>>>>> Hi Suzuki,
>>>>>
>>>>> This issue happens when race condition happens.
>>>>> The condition is that the device and its child_device's probe 
>>>>> happens at the same time.
>>>>>
>>>>> For example: device0 and its child device device1.
>>>>> Both of them are calling coresight_register function. device0 is 
>>>>> calling coresight_fixup_device_conns.
>>>>> device1 is waiting for device0 to release the coresight_mutex. 
>>>>> Because device1's csdev node is allocated,
>>>>> coresight_make_links will be called for device0. Then in 
>>>>> coresight_add_sysfs_link, has_conns_grp is true
>>>>> for device0, but has_conns_grp is false for device1 as 
>>>>> has_conns_grp is set to true in coresight_create_conns_sysfs_group .
>>>>> The probe of device0 will fail for at this condition.
>>>>>
>>>>>
>>>>> struct coresight_device *coresight_register(struct coresight_desc 
>>>>> *desc)
>>>>> {
>>>>>     .........
>>>>>      mutex_lock(&coresight_mutex);
>>>>>
>>>>>      ret = coresight_create_conns_sysfs_group(csdev);
>>>>>      if (!ret)
>>>>>          ret = coresight_fixup_device_conns(csdev);
>>>>>      if (!ret)
>>>>>          ret = coresight_fixup_orphan_conns(csdev);
>>>>>      if (!ret && cti_assoc_ops && cti_assoc_ops->add)
>>>>>          cti_assoc_ops->add(csdev);
>>>>>
>>>>>      mutex_unlock(&coresight_mutex);
>>>>>
>>>>> .........
>>>>>
>>>>> }
>>>>>
>>>>> static int coresight_fixup_device_conns(struct coresight_device 
>>>>> *csdev)
>>>>> {
>>>>>     ..........
>>>>>          conn->child_dev =
>>>>> coresight_find_csdev_by_fwnode(conn->child_fwnode);
>>>> The issue appears to be a constraint hidden in the lower layers of 
>>>> the code.
>>>> Would a better solution not be to alter the code here:
>>>>
>>>> if (conn->child_dev && conn->child_dev->has_conns_grp) {
>>>>     ...
>>>> } else {
>>>>        csdev->orphan = true;
>>>> }
>>>>
>>>> which would mean that the connection attempt would drop through to
>>>> label the connection as an orphan, to be cleaned up by the child
>>>> itself when it runs coresight_fixup_orphan_conns()
>>>>
>>
>> Tnanks Mike, I think that is a good solution. Alternatively, we
>> could make sure that device_register() and the fixup following
>> that are atomic.
>>
>> i.e.
>>
>>     mutex_lock()
>>
>>     device_register()
>>     fixup_connections()
>>     create_sysfs()
>>
>>     mutex_unlock();
>>
>> The fix may be a bit invasive than Mike's proposal, but it makes
>> sure we don't end up with half baked device on the coresight-bus.
>>
>> Suzuki
>
> Thanks Mike & Suzuki.
>
> I will combine your proposals and make the changes.
>
> I will get back to you after the test.

Hi Mike & Suzuki,

Issue is fixed with your proposal.
I submit a new patch "coresight: core: Fix coresight device probe 
failure issue".
Please help to review.

Thanks
Jinlong Mao
>
>
> Thanks
> Jinlong Mao
>