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

[Boris Brezillon]

On Mon, 26 Nov 2018 14:25:44 +0100
Miquel Raynal <miquel.raynal at bootlin.com> wrote:

> Hi Jagan,
> 
> Jagan Teki <jagan at 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 at bootlin.com> wrote:
> > >   
> > >> On Mon, 26 Nov 2018 16:42:48 +0530
> > >> Jagan Teki <jagan at 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 at 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.

Jagan, are you okay with this suggestion (add a debug() message in the
del_mtd_device() path and keep the one we already have in sf_mtd.c)?