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

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Message-ID: <CALAqxLVCpyKzGJPVtBuipnZbGbDC_Z0rPBrn-J2mkMsQsSvdtA@mail.gmail.com>
Date:   Tue, 12 Jun 2018 15:40:41 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Thomas Richter <tmricht@...ux.ibm.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: REGRESSION?: debugfs: inode: debugfs_create_dir uses mode permission
 from parent

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.

This seems to be the expected behavior of the patch, but I'm surprised
the mode override is now ignored. It seems like the potential fix here
would be to set the /sys/kernel/debug dir to 755 prior to mounting? Or
is there some other advised solution?

thanks
-john