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

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Date:   Fri, 26 Jul 2019 15:44:40 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Leo Yan <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 3:14 PM, Sai Prakash Ranjan wrote:
> On 7/26/2019 2:11 PM, 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 am not mounting devtmpfs. However
> 
>   CONFIG_DEVTMPFS=y
>   CONFIG_DEVTMPFS_MOUNT=y
> 

Ok my initramfs is using mdev:

*/sbin/mdev -s*

This somehow is not mounting etr, etf, stm devices when uevent-helper is
disabled. Anyways as Suzuki mentioned, using devtmpfs does fix the issue.

Thanks,
Sai

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