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

[Helge Deller]

Hi Lorenzo,

On 10/12/26 18:48, Lorenzo Stoakes (ARM) wrote:
> 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@xxxxxxxxxx>
> > ---
> > 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!

Thank you for those patches!
I've applied them now to the fbdev/for-next git tree.

> 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.
Yes, but still I hesitate to push it for 7.3, as it seems quite unlikely
that a normal installation will run into this memory leak.
So, I think this can wait for 7.4-rc1, right?

Helge