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Date:   Tue, 11 Feb 2020 11:01:27 +0000
From:   Will Deacon <will@kernel.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     "Theodore Y. Ts'o" <tytso@mit.edu>,
        Jonathan Corbet <corbet@lwn.net>,
        Saravana Kannan <saravanak@google.com>,
        Jason Baron <jbaron@akamai.com>, linux-kernel@vger.kernel.org,
        kernel-team@android.com, Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v6] dynamic_debug: allow to work if debugfs is disabled
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On Mon, Feb 10, 2020 at 01:11:42PM -0800, Greg Kroah-Hartman wrote:
> With the realization that having debugfs enabled on "production" systems
> is generally not a good idea, debugfs is being disabled from more and
> more platforms over time.  However, the functionality of dynamic
> debugging still is needed at times, and since it relies on debugfs for
> its user api, having debugfs disabled also forces dynamic debug to be
> disabled.
> 
> To get around this, also create the "control" file for dynamic_debug in
> procfs.  This allows people turn on debugging as needed at runtime for
> individual driverfs and subsystems.
> 
> Reported-by: many different companies
> Cc: Jason Baron <jbaron@akamai.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> v6: fix up Kconfig help, it was a bit incorrect,thanks to Saravana for
>     the review.
> v5: as many people asked for it, now enable the control file in both
>     debugfs and procfs at the same time.

The 'ddebug_lock' mutex looks like it resolves all of the races here, so:

Acked-by: Will Deacon <will@kernel.org>

Will