Re: Another memory leak in drivers/char/vt.c

Catalin Marinas
2009-07-29T11:04:33Z

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