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

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Date:   Fri, 26 Jul 2019 13:50:27 +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 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*

Thanks,
Sai

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