linux-kernel - Re: [patch] fbcon: don't use vc

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Date:	Fri, 31 Jul 2009 10:09:15 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>, penberg@...helsinki.fi,
	linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net
Subject: Re: [patch] fbcon: don't use vc_resize() on initialization

On Thu, 2009-07-30 at 16:11 -0700, Andrew Morton wrote:
> On Wed, 29 Jul 2009 19:21:23 +0200
> Johannes Weiner <hannes@...xchg.org> wrote:
> 
> > Catalin and kmemleak spotted a leak of a VC screen buffer in
> > vc_allocate() due to the following chain of events:
> > 
> > 	vc_allocate()
> > 	  visual_init(init=1)
> > 	    vc->vc_sw->con_init(init=1)
> >               fbcon_init()
> > 	        vc_resize()
> > 	          vc->screen_buf = kmalloc()
> > 	  vc->screen_buf = kmalloc()
> > 
> > The common way for the VC drivers is to set the screen dimension
> > parameters manually in the init case and only call vc_resize() for
> > !init - which allocates a screen buffer according to the new
> > dimensions.
> > 
> > fbcon instead would do vc_resize() unconditionally and afterwards set
> > the dimensions manually (again) for !init - i.e. completely upside
> > down.  The vc_resize() allocated buffer would then get lost by
> > vc_allocate() allocating a fresh one.
> > 
> > Use vc_resize() only for actual resizing to close the leak.
> > 
> > Set the dimensions manually only in initialization mode to remove the
> > redundant setting in resize mode.
> > 
> > The kmemleak trace from Catalin:
> > 
> > unreferenced object 0xde158000 (size 12288):
> 
> That's a big leak!
> 
> What sequence of user actions would cause it to occur?

In my case, I think anything that causes a tty_open() call with a
framebuffer console. I get a leak when logging in on the console and
another when starting the X server.

-- 
Catalin

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