There's a callchain of:

fbcon_fb_blanked -> do_(un)blank_screen -> consw->con_blank
	-> fbcon_blank -> fb_blank

Things don't go horribly wrong because the BKL console_lock safes the
day, but that's about it. And the seeming recursion is broken in 2
ways:
- Starting from the fbdev ioctl we set FBINFO_MISC_USEREVENT, which
  tells the fbcon_blank code to not call fb_blank. This was required
  to not deadlock when recursing on the fb_notifier_chain mutex.
- Starting from the con_blank hook we're getting saved by the
  console_blanked checks in do_blank/unblank_screen. Or at least
  that's my theory.

Anyway, recursion isn't awesome, so let's stop it. Breaking the
recursion avoids the need to be in the FBINFO_MISC_USEREVENT critical
section, so lets move it out of that too.

The astute reader will notice that fb_blank seems to require
lock_fb_info(), which the fbcon code seems to ignore. I have no idea
how to fix that problem, so let's keep ignoring it.

v2: I forgot the sysfs blanking code.

v3: Fix typo in callchain in the commmit message (Sam).
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: Peter Rosin <peda@axentia.se>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Rob Clark <robdclark@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-26-daniel.vetter@ffwll.ch