linux-kernel - Re: [Regression] Missing device nodes for ETR, ETF and STM after CONFIG_UEVENT

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Date:   Fri, 26 Jul 2019 15:32:20 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        gregkh@...uxfoundation.org
Cc:     geert+renesas@...der.be, mathieu.poirier@...aro.org,
        leo.yan@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [Regression] Missing device nodes for ETR, ETF and STM after
 CONFIG_UEVENT_HELPER=n

On 7/26/2019 3:28 PM, Sai Prakash Ranjan wrote:
> Hi Suzuki,
> 
> On 7/26/2019 2:58 PM, Suzuki K Poulose wrote:
>>
>>
>> On 07/26/2019 09:41 AM, Greg Kroah-Hartman wrote:
>>> On Fri, Jul 26, 2019 at 01:50:27PM +0530, Sai Prakash Ranjan wrote:
>>>> On 7/26/2019 12:34 PM, Greg Kroah-Hartman wrote:
>>>>> On Fri, Jul 26, 2019 at 11:49:19AM +0530, Sai Prakash Ranjan wrote:
>>>>>> Hi,
>>>>>>
>>>>>> When trying to test my coresight patches, I found that etr,etf and 
>>>>>> stm
>>>>>> device nodes are missing from /dev.
>>>>>
>>>>> I have no idea what those device nodes are.
>>>>>
>>>>>> Bisection gives this as the bad commit.
>>>>>>
>>>>>> 1be01d4a57142ded23bdb9e0c8d9369e693b26cc is the first bad commit
>>>>>> commit 1be01d4a57142ded23bdb9e0c8d9369e693b26cc
>>>>>> Author: Geert Uytterhoeven <geert+renesas@...der.be>
>>>>>> Date:   Thu Mar 14 12:13:50 2019 +0100
>>>>>>
>>>>>>       driver: base: Disable CONFIG_UEVENT_HELPER by default
>>>>>>
>>>>>>       Since commit 7934779a69f1184f ("Driver-Core: disable 
>>>>>> /sbin/hotplug by
>>>>>>       default"), the help text for the /sbin/hotplug fork-bomb says
>>>>>>       "This should not be used today [...] creates a high system 
>>>>>> load, or
>>>>>>       [...] out-of-memory situations during bootup".  The 
>>>>>> rationale for this
>>>>>>       was that no recent mainstream system used this anymore (in 
>>>>>> 2010!).
>>>>>>
>>>>>>       A few years later, the complete uevent helper support was 
>>>>>> made optional
>>>>>>       in commit 86d56134f1b67d0c ("kobject: Make support for 
>>>>>> uevent_helper
>>>>>>       optional.").  However, if was still left enabled by default, 
>>>>>> to support
>>>>>>       ancient userland.
>>>>>>
>>>>>>       Time passed by, and nothing should use this anymore, so it 
>>>>>> can be
>>>>>>       disabled by default.
>>>>>>
>>>>>>       Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>>>>>>       Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>>>>
>>>>>>    drivers/base/Kconfig | 1 -
>>>>>>    1 file changed, 1 deletion(-)
>>>>>>
>>>>>>
>>>>>> Any idea on this?
>>>>>
>>>>> That means that who ever created those device nodes is relying on udev
>>>>> to do this, and is not doing the correct thing within the kernel and
>>>>> using devtmpfs.
>>>>>
>>>>> Any pointers to where in the kernel those devices are trying to be
>>>>> created?
>>>>>
>>>>
>>>> Somewhere in drivers/hwtracing/coresight/* probably. I am not sure,
>>>> Mathieu/Suzuki would be able to point you to the exact code.
>>>>
>>>> Also just to add on some more details, I am using *initramfs*
>>
>>>
>>> Are you using devtmpfs for your /dev/ mount?
>>
>> I think that should solve the issue ^^
>>
> 
> Yes mounting /dev using devtmpfs does solve the issue. But is this 
> different behaviour OK?

Sorry ignore the different behaviour thing. I misunderstood.

-Sai

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