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Date:   Fri, 26 Jul 2019 10:41:27 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc:     Geert Uytterhoeven <geert+renesas@glider.be>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Leo Yan <leo.yan@linaro.org>, linux-arm-msm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [Regression] Missing device nodes for ETR, ETF and STM after
 CONFIG_UEVENT_HELPER=n
Message-ID: <20190726084127.GA28470@kroah.com>
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 <20190726070429.GA15714@kroah.com>
 <165028a7-ff12-dd28-cc4c-57a3961dbb40@codeaurora.org>
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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@glider.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@glider.be>
> > >      Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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?

If you enable this option, what does:
	ls -l /dev/etr
	ls -l /dev/etf
	ls -l /dev/stm
result in?

What are these device nodes for?  Are they symlinks?  Real devices that
show up in /sys/dev/char/ as a real value?  Or something else?

Do you have udev rules that create these nodes somehow?

thanks,

greg k-h