gpmc-nand broken since v4.12

[Boris Brezillon]

On Mon, 16 Oct 2017 15:12:38 +0300
Roger Quadros <rogerq at ti.com> wrote:

> Hi Boris,
> 
> 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
> 
> On 16/10/17 14:34, Boris Brezillon wrote:
> > Hi Roger,
> > 
> > On Mon, 16 Oct 2017 13:22:04 +0300
> > Roger Quadros <rogerq at ti.com> wrote:
> >   
> >> 
> >> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
> >>
> >> On 13/10/17 23:29, Boris Brezillon wrote:  
> >>> On Fri, 13 Oct 2017 22:24:58 +0200
> >>> Boris Brezillon <boris.brezillon at free-electrons.com> wrote:
> >>>     
> >>>> On Fri, 13 Oct 2017 14:50:33 +0200
> >>>> Boris Brezillon <boris.brezillon at free-electrons.com> wrote:
> >>>>    
> >>>>> On Fri, 13 Oct 2017 14:57:29 +0300
> >>>>> Roger Quadros <rogerq at ti.com> wrote:
> >>>>>       
> >>>>>> Hi Boris,
> >>>>>>
> >>>>>> NAND on gpmc-omap breaks for me while doing a unmount of a ubi volume since v4.12
> >>>>>>
> >>>>>> Behaviour follows through in v4.13 and v4.14-rc as well.
> >>>>>>
> >>>>>> Do you have any idea about this?      
> >>>>
> >>>> More info on what has changed in 4.12: we no longer allocate the
> >>>> nand_buffer struct + its internal buffer using a single big kmalloc
> >>>> call, which means the nand_buffer struct is now likely to be allocated
> >>>> in a small object slab (sizeof(nand_buffers) = 12). If you have a
> >>>> use-after-free bug somewhere in the kernel, it might corrupt the    
> >>
> >> Spot on. Problem starts from commit 4d5dea5725f3aa95b9b64e252540e435dd216dbc
> >> "mtd: nand: allocate aligned buffers if NAND_OWN_BUFFERS is unset"
> >>  
> >>>
> >>> I meant buffer-overflow, not use-after-free.    
> >>
> >> Your analysis seems correct.
> >>  
> >>>     
> >>>> nand_buffers object, which might explain the bug you see here.
> >>>>    
> >>>>>
> >>>>> Can you try with this patch [1] applied and paste me the values printed
> >>>>> just before the crash?
> >>>>>
> >>>>> [1]http://code.bulix.org/lc8xk0-209746    
> >>
> >> == unmounting volume
> >> [   36.308792] nand: nand_write_subpage_hwecc:2575 ecc_calc =   (null) oob_poi = ed096800
> >> [   36.317319] mtd_ooblayout_set_bytes:1330 dst = ed096802 src =   (null)
> >> [   36.324162] Unable to handle kernel NULL pointer dereference at virtual address 00000000
> >>
> >>
> >> Running the following patch
> >> https://hastebin.com/ulogurutuz.php
> >> shows
> >>
> >> [   37.260689] nand: nand_write_subpage_hwecc:2547:A ecc_calc = ed116e40 oob_poi = ed117800
> >> [   37.260772] nand: nand_write_subpage_hwecc:2556:A1:step 0, ecc_calc = ed116e40
> >> [   37.260779] nand: nand_write_subpage_hwecc:2562:A2:step 0, ecc_calc = ed116e40
> >> [   37.260834] nand: nand_write_subpage_hwecc:2556:A1:step 1, ecc_calc = ed116e40
> >> [   37.260840] nand: nand_write_subpage_hwecc:2567:A3-pre:step 1, ecc_calc = ed116e40
> >> [   37.260846] omap_calculate_ecc_bch
> >> [   37.260856] nand: nand_write_subpage_hwecc:2570:A3-post:step 1, ecc_calc =   (null)
> >> [   37.260912] nand: nand_write_subpage_hwecc:2556:A1:step 2, ecc_calc =   (null)
> >> [   37.260918] nand: nand_write_subpage_hwecc:2562:A2:step 2, ecc_calc =   (null)
> >> [   37.260972] nand: nand_write_subpage_hwecc:2556:A1:step 3, ecc_calc =   (null)
> >> [   37.260978] nand: nand_write_subpage_hwecc:2562:A2:step 3, ecc_calc =   (null)
> >> [   37.260984] nand: nand_write_subpage_hwecc:2587:B ecc_calc =   (null) oob_poi = ed117800
> >> [   37.260991] mtd_ooblayout_set_bytes:1330 dst = ed117802 src =   (null)
> >>
> >> which means omap_calculate_ecc_bch() it the culprit.
> >>
> >> Looks like the function calculates and stores ECC for all sectors even if we just want ECC
> >> for just one sector (sub-page).  
> > 
> > Yes, looks like you find the root cause.
> >   
> >>
> >> Is my understanding correct
> >> - We should not be hooking the multi-sector ECC calculator omap_calculate_ecc_bch() to ecc.calculate
> >> - provide a new one sector ECC calculator function (for BCH4/8/16) for omap and hook it to ecc.calculate
> >> OR
> >> - override nand_read_subpage() and nand_write_subpage() using omap specific implementation (for BCH4/8/16).  
> > 
> > Second solution sounds simpler because the ECC sector information is
> > not passed to ecc->calculate() hook, which means you'd have to extract
> > it from the ecc_calc pointer:
> > 
> > 	(uintptr_t)(ecc_calc - chip->buffers->ecccalc) / chip->ecc.size  
> 
> I don't think we need ECC sector number at all if we're always going to do a transfer
> of one sector of data after calling ecc.hwctl(NAND_ECC_READ/WRITE) and before calling ecc.calculate.
> 
> My understanding is that the ECC calculators sector 0 registers will always contain
> the right content irrespective of which sector we transfer as long as we do,
> 	ecc.hwctl(mtd, NAND_ECC_READ/WRITE);
> 	transfer one sector;
> 	ecc.calculate();

Ok, then the first solution sounds good too.

> 
> Why isn't there a nand_read_subpage_hwecc()?

Probably because nobody ever needed it. Feel free to add it if you
think this is necessary.

> In the current form a subpage read won't work if
> if ecc->mode is NAND_ECC_HW and controllers expect a ecc.hwctl(NAND_ECC_READ) before
> calling ecc.calculate().
> 
> For the OMAP case I can override both subpage functions.
> Is there a good way to test if subpage read/writes are working as they should?

There's a nandsubpage test [1] in mtd-utils.

[1]http://git.infradead.org/mtd-utils.git/blob/HEAD:/tests/mtd-tests/nandpagetest.c