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    SubjectRe: [patch] fbcon: don't use vc_resize() on initialization
    On Wed, 29 Jul 2009 19:21:23 +0200
    Johannes Weiner <hannes@cmpxchg.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?

    > 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
    >
    > Reported-by: Catalin Marinas <catalin.marinas@arm.com>
    > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
    > Tested-by: Catalin Marinas <catalin.marinas@arm.com>
    > Cc: Pekka Enberg <penberg@cs.helsinki.fi>
    > ---
    > drivers/video/console/fbcon.c | 6 +++---
    > 1 files changed, 3 insertions(+), 3 deletions(-)
    >
    > diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
    > index 471a9a6..3a44695 100644
    > --- a/drivers/video/console/fbcon.c
    > +++ b/drivers/video/console/fbcon.c
    > @@ -1082,7 +1082,6 @@ static void fbcon_init(struct vc_data *vc, int init)
    > new_rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
    > new_cols /= vc->vc_font.width;
    > new_rows /= vc->vc_font.height;
    > - vc_resize(vc, new_cols, new_rows);
    >
    > /*
    > * We must always set the mode. The mode of the previous console
    > @@ -1111,10 +1110,11 @@ static void fbcon_init(struct vc_data *vc, int init)
    > * vc_{cols,rows}, but we must not set those if we are only
    > * resizing the console.
    > */
    > - if (!init) {
    > + if (init) {
    > vc->vc_cols = new_cols;
    > vc->vc_rows = new_rows;
    > - }
    > + } else
    > + vc_resize(vc, new_cols, new_rows);
    >
    > if (logo)
    > fbcon_prepare_logo(vc, info, cols, rows, new_cols, new_rows);



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