[U-Boot] [PATCH v3 11/11] mtd: sf: Make sf_mtd.c more robust

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Jagan,

Jagan Teki <jagan@openedev.com> wrote on Mon, 26 Nov 2018 18:35:01
+0530:

> On 26/11/18 6:12 PM, Boris Brezillon wrote:
> > On Mon, 26 Nov 2018 13:37:46 +0100
> > Boris Brezillon <boris.brezillon@bootlin.com> wrote:
> > 
> >> On Mon, 26 Nov 2018 16:42:48 +0530
> >> Jagan Teki <jagan@openedev.com> wrote:
> >>
> >>> On 26/11/18 2:12 PM, Boris Brezillon wrote:
> >>>> Hi Jagan,
> >>>>
> >>>> On Thu, 22 Nov 2018 09:40:56 +0100
> >>>> Boris Brezillon <boris.brezillon@bootlin.com> wrote:
> >>>>      >>>>>>> +       /*
> >>>>>>> +        * Setting mtd->priv to NULL is the best we can do. Thanks to that,
> >>>>>>> +        * the MTD layer can still call mtd hooks without risking a
> >>>>>>> +        * use-after-free bug. Still, things should be fixed to prevent the
> >>>>>>> +        * spi_flash object from being destroyed when del_mtd_device() fails.
> >>>>>>> +        */
> >>>>>>> +       sf_mtd_info.priv = NULL;
> >>>>>>> +       printf("Failed to unregister MTD %s and the spi_flash object is going away: you're in deep trouble!",
> >>>>>>> +              sf_mtd_info.name);
> >>>>>>
> >>>>>> Why do we need this print?
> >>>>>
> >>>>> Yes we do, just to keep the user informed that something bad happened
> >>>>> and its spi-flash is no longer usable (at least through the MTD layer).
> >>>>>     >>>>>> can't we do the same thing in MTD core
> >>>>>> itself, so-that it can be generic for all flash objects.
> >>>>>
> >>>>> del_mtd_device() can fail, so it's the caller responsibility to decide
> >>>>> what to do when that happens. Some users will propagate the error to
> >>>>> the upper layer and maybe cancel the device removal (AFAICT,
> >>>>> driver->remove() can return an error, not sure what happens in this
> >>>>> case though). For others, like spi-flash, the device will go away, and
> >>>>> all subsequent accesses will fail.
> >>>>
> >>>> I'm about to send a new version fixing the problem I mentioned in patch
> >>>> 3, but before doing that, I'd like to know if my answer convinced you or
> >>>> if you'd still prefer this message to go away (or be placed in
> >>>> mtdcore/mtdpart.c).
> >>>
> >>>
> >>> I'm thinking of having the message still in MTD by showing which
> >>> interface it would belongs, along with the details.
> >>
> >> Then we'd need something less
> > 
> > Sorry, I inadvertently hit the send button :-/.
> > 
> > So, I was about to say that we need something less worrisome than the
> > message I added in the SF layer if we move it to the MTD layer because
> > some drivers might actually do the right thing when del_mtd_device()
> > returns an error. I keep thinking that putting an error message in
> > mtdcore.c is not the right thing to do, but if you insist, I'll add
> > one (maybe a debug()). In any case I'd like to keep the one we have
> > here, because in this specific case, there's simply nothing we can do
> > when MTD dev removal fails.
> > 
> 
> Look like other flashes were deleting only via mtd_partitions. how would they know and does it not need for them to print the same information?

Do you see that sf does not use MTD in a consistent manner? The whole
point of this commit is to handle sf's lightnesses in a "more robust"
manner. This warning belongs to sf and not to the mtdcore, because
as stated in the comment above, we should "prevent the spi_flash
object from being destroyed when del_mtd_device() fails". If you don't
want such warning in sf, I think the best thing to do is to fix the
root issue.


Thanks,
Miquèl