On Mon, 16 Oct 2017 14:39:04 +0200 Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> wrote: > On Mon, 16 Oct 2017 15:12:38 +0300 > Roger Quadros <rogerq@xxxxxx> 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@xxxxxx> 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@xxxxxxxxxxxxxxxxxx> wrote: > > >>> > > >>>> On Fri, 13 Oct 2017 14:50:33 +0200 > > >>>> Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> wrote: > > >>>> > > >>>>> On Fri, 13 Oct 2017 14:57:29 +0300 > > >>>>> Roger Quadros <rogerq@xxxxxx> 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. Actually, if you want to make your patch easily backport-able to stable releases, you'd better go for the omap_nand_write/read_subpage() approach. The generic solution can be done afterwards. > > > 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 > > ______________________________________________________ > Linux MTD discussion mailing list > http://lists.infradead.org/mailman/listinfo/linux-mtd/ -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
