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

[Andrea Righi]

On Thu, Apr 09, 2009 at 07:36:24PM +0800, Eric Miao wrote:
> This happens on my Marvell PXA310-based Littleton platform with
> Angstrom Distribution. The offending paths are many:
> 
> FBIOPUT_VSCREENINFO:
>   lock_fb_info()
>   --> fb_set_var()
>     --> fb_notifier_call_chain() [FBINFO_MISC_USEREVENT]
>       --> fbcon_event_notifier() [FB_EVENT_MODE_CHANGE]
>         --> lock_fb_info()
> 
> OK, now hang. I'd suggest a clean fix to the original assumption of
> circular locking
> issue and revert this commit first.
> 
> -- 
> Cheers
> - eric

I can agree to revert 66c1ca019078220dc1bf968f2bb18421100ef147, since I
don't have a clean fix for this. Pushing down fb_info->lock in
fb_set_var() excluding to call fb_notifier_call_chain with fb_info->lock
held doesn't seem to be so trivial...

However, reverting this will re-introduce the circular locking
dependency fb_info->lock => mm->mmap_sem => fb_info->lock.

-Andrea
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