Re: [PATCH 0/6] fbdev: fixup callers which ignore errors from fb_deferred_io_init()

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Sat, Sep 26, 2026 at 02:16:58PM +0100, Lorenzo Stoakes (ARM) wrote:
> Commit 56c134f7f1b5 ("fbdev: Track deferred-I/O pages in pageref struct")
> converted fb_deferred_io_init() from a void function to one returning an
> error value.
>
> However a number of callers don't seem to have been apprised of the fact
> and continue to treat it like a void function.
>
> This is problematic, as upon allocation failure, struct
> fb_info->fbdefio_state is NULL.
>
> That means when a subsequent operation is performed upon the driver, for
> instance opening the file, a NULL pointer dereference occurs.
>
> Update all of the remaining drivers which fail to check this to do so.
>
> This issue was discovered as part of a separate series which updated logic
> belonging to ssd1307fb.
>
> Also fix up a separate issue with a BUG_ON() occurring on allocation
> failure for udlfb and smcufx.
>
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> ---
> Lorenzo Stoakes (ARM) (6):
>       fbdev: ssd1307fb: check for fb_deferred_io_init() error
>       fbdev: xen-fbfront: check for fb_deferred_io_init() error
>       HID: picoLCD: check for fb_deferred_io_init() error
>       fbdev: udlfb: check for fb_deferred_io_init() error
>       fbdev: smscufx: check for fb_deferred_io_init() error
>       fbdev: sh_mobile_lcdc: check for fb_deferred_io_init() error

Ping on this!

I know timing is awful given a. the insane volume this cycle and b. LPC,
but these are fairly mechanical things so should be relatively
straightforward.

>
>  drivers/hid/hid-picolcd_fb.c           | 12 +++++++++---
>  drivers/video/fbdev/sh_mobile_lcdcfb.c |  6 +++++-
>  drivers/video/fbdev/smscufx.c          |  9 ++++++---
>  drivers/video/fbdev/ssd1307fb.c        |  6 +++++-
>  drivers/video/fbdev/udlfb.c            |  9 ++++++---
>  drivers/video/fbdev/xen-fbfront.c      |  7 ++++++-
>  6 files changed, 37 insertions(+), 12 deletions(-)
> ---
> base-commit: 6812ce4e4379ffc99c52401ec28f0d7ffbc36206
> change-id: 20260926-fix-fbdefio-error-handling-ab135b0193cb
>
> Best regards,
> --
> Lorenzo Stoakes (ARM) <ljs@kernel.org>
>

--
Cheers, Lorenzo