linux-kernel - Re: REGRESSION?: debugfs: inode: debugfs_create

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Message-ID: <20180613045853.GB1246@kroah.com>
Date:   Wed, 13 Jun 2018 06:58:53 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Thomas Richter <tmricht@...ux.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: REGRESSION?: debugfs: inode: debugfs_create_dir uses mode
 permission from parent

On Tue, Jun 12, 2018 at 03:40:41PM -0700, John Stultz wrote:
> Hey all,
>   I noticed recently that linus/master (plus patches) stopped booting
> to UI on HiKey960, and I bisected the issue down to:
> 92170b62f1c1 ("debugfs: inode: debugfs_create_dir uses mode permission
> from parent")
> 
> On the HiKey960 board, we mount debugfs via:
>    mount debugfs /sys/kernel/debug /sys/kernel/debug mode=755
> 
> But since the change, it seems most of the nodes in /sys/kernel/debug
> are: drwx------
> 
> Which ends up breaking the egl library, keeping it from loading.

While the debugfs change is now reverted in Linus's tree, I find it
"odd" that a debugfs change would cause egl from loading entirely.  No
userspace code should depend on debugfs files being there or not.  If it
does, that's a bug as debugfs is for _debugging_ stuff, it should not be
an interface between user/kernel that userspace requires for basic
functionality like booting.

And yes, I know all about the crazy qualcom batter api, where they
shoved it into debugfs and ignored the built-in kernel api, that should
be fixed now.  If this is a new one-of-those types of problem, I need to
know so it can get resolved.

thanks,

greg k-h