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Subject: Re: Another memory leak in drivers/char/vt.c
From: Catalin Marinas <catalin.marinas@arm.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>,
       linux-kernel <linux-kernel@vger.kernel.org>
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Organization: ARM Ltd
Date: Wed, 29 Jul 2009 12:04:16 +0100
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On Wed, 2009-07-29 at 12:39 +0200, Johannes Weiner wrote:
> On Wed, Jul 29, 2009 at 10:31:23AM +0100, Catalin Marinas wrote:
> > There was a memory leak fixed recently by commit 1a8f458f6d. However,
> > there seems to be another with this kmemleak trace:
> > 
> > unreferenced object 0xde158000 (size 12288):
> >   comm "Xorg", pid 1439, jiffies 4294961016
> >   hex dump (first 32 bytes):
> >     20 00 20 00 20 00 20 00 20 00 20 00 20 00 20 00   . . . . . . . .
> >     20 00 20 00 20 00 20 00 20 00 20 00 20 00 20 00   . . . . . . . .
> >   backtrace:
> >     [<c006f74b>] __save_stack_trace+0x17/0x1c
> >     [<c006f81d>] create_object+0xcd/0x188
> >     [<c01f5457>] kmemleak_alloc+0x1b/0x3c
> >     [<c006e303>] __kmalloc+0xdb/0xe8
> >     [<c012cc4b>] vc_do_resize+0x73/0x1e0
> >     [<c012cdf1>] vc_resize+0x15/0x18
> >     [<c011afc1>] fbcon_init+0x1f9/0x2b8
> >     [<c0129e87>] visual_init+0x9f/0xdc
> >     [<c012aff3>] vc_allocate+0x7f/0xfc
> >     [<c012b087>] con_open+0x17/0x80
> >     [<c0120e43>] tty_open+0x1f7/0x2e4
> >     [<c0072fa1>] chrdev_open+0x101/0x118
> >     [<c006ffad>] __dentry_open+0x105/0x1cc
> >     [<c00700fd>] nameidata_to_filp+0x2d/0x38
> >     [<c00788cd>] do_filp_open+0x2c1/0x54c
> >     [<c006fdff>] do_sys_open+0x3b/0xb4
> > 
> > The problem happens in the vc_allocate() function where vc->vc_screenbuf
> > is set to the kmalloc() returned value. However, the visual_init()
> > function called 3 lines before also allocates the vc->vc_screenbuf.
> 
> The common way seems to be that ->con_init(init=1) just sets the
> dimensions manually (instead of using vc_resize()) and vc_allocate()
> uses them to actually allocate a properly sized screen buffer.
> 
> So it seems like fbcon is at fault here.  It calls vc_resize() from
> ->con_init(init=1) and updates the console dimensions manually on
> init=0 (after calling vc_resize()) which is completely mixed up.
> 
> I think the quick fix is something like the appended (untested!).

This patch seems to fix the leak, you can add

Tested-by: Catalin Marinas <catalin.marinas@arm.com>

Thanks.

-- 
Catalin