Re: [REGRESSION] commit 66c1ca0: {fbmem: fix fb_info->lock and mm->mmap_sem ...} causes Xfbdev not working

[Andrea Righi <righi.andrea@gmail.com>]

On Sat, Apr 11, 2009 at 11:21:31AM -0700, Andrew Morton wrote:
> On Sat, 11 Apr 2009 17:04:00 +0200 Andrea Righi <righi.andrea@gmail.com> wrote:
> 
> > fbdev: fix info->lock deadlock in fbcon_event_notify()
> > 
> > fb_notifier_call_chain() is called with info->lock held, i.e. in
> > do_fb_ioctl() => FBIOPUT_VSCREENINFO => fb_set_var() and the some
> > notifier callbacks, like fbcon_event_notify(), try to re-acquire
> > info->lock again.
> > 
> > Remove the lock/unlock_fb_info() in all the framebuffer notifier
> > callbacks' and be sure to always call fb_notifier_call_chain() with
> > info->lock held.
> 
> Thanks.  So do you think we should proceed with this patch instead of
> reverting 66c1ca0?

Yes, there's no need to revert 66c1ca0 now, otherwise we'll simply
reintroduce the info->lock / mm->mmap_sem circular locking dependency.

I'd like to test the fbdev mode switching, but it seems intelfb doesn't
support it with LVDS ports (and at the moment I've not a CRT here...).

Anyway, if someone will have troubles with mode switching I'm quite sure
we can fix it on top of this patch.

-Andrea